(CNN) Gun attacks, remotely detonated bombs and even drones carrying explosives and chemical weapons: These are just a few of the terrorist threats French authorities are preparing for at the Euro 2016 football championship, which gets underway on Friday.

Just days before the championship kicks off, Ukraine security services said they had arrested a Frenchman and an accomplice who were planning attacks on French targets before and during the tournament. The arrests are a reminder that the soccer tournament faces more terrorism threats than just ISIS.

The U.S. State Department has issued a warning about the potential terror risk associated the tournament, and on Wednesday, British Prime Minister David Cameron in parliament described the threat at the event as "severe." He said the half a million people expected to travel from Britain to France for the championship should be aware of the threat level.

Cameron said: "This is a very big security undertaking. We have set out very clear travel advice because people do need to know that obviously there is a significant terror threat in France today and there is a potential threat to this tournament."

"The French security operation is enormous," he added.

Britain's Foreign Office issued a new travel advisory for France on Tuesday, warning of a "high threat from terrorism," specifically associated with ISIS.

Terror alert app

The French Interior Ministry has launched an app called #SAIP -- a French acronym for Alert and Information System for the Public -- to alert users to any possible terror attacks or incidents nearby.

The app will give "behavioral advice" and "instructions adapted to the nature of the alert," the ministry explained on Twitter.

Le ministère de l'Intérieur lance un nouveau système d'#alerte et d'information de la population #SAIP pic.twitter.com/8jQHyBg5x4 — Ministère Intérieur (@Place_Beauvau) 8 June 2016

"During Euro 2016, stadiums, fan zones, venues broadcasting the tournament and transport hubs and links represent potential targets for terrorist attacks," says the advisory.

"You should be vigilant at all times, especially in areas hosting Euro 2016 events, and follow the advice of local French authorities."

Ukraine arrests suspects who wanted to attack Euro 2016.

As President Francois Hollande and other French officials have acknowledged, 100% security and zero risk are impossible to guarantee. ISIS has made clear its intent to attack the tournament.

In a radio interview with France Info on Sunday, Hollande said: "We have invested all the means to succeed, and we must not allow ourselves to be pressured by the threat." But he cautioned: "It exists, this threat."

France has extended its state of emergency, introduced after the terror attacks in Paris last November, until the end of July. It gives police greater powers of house arrest and allows for demonstrations and rallies to be banned.

51 games, 10 venues

The task of securing a major sporting event that will attract several million fans from across the continent and feature 51 games at 10 venues is immense.

Nearly 100,000 French security forces will be deployed to safeguard the tournament, at match venues, fan zones and in other areas where fans will congregate.

The bases of the 24 competing countries will be heavily guarded and have been declared no-fly zones, as have the stadiums.

Authorities have also introduced technology around venues that's designed to take control of and divert suspect drones rather than destroy them, according to security sources.

Photos: Euro 2016 draw: 24 teams await fate After more than a year of qualifying matches, 23 teams as well as host nation France will fight it out at Euro 2016 -- the continent's biggest football party. The 24 teams discovered Saturday who they will play after the draw in the Palais des Congres. Hide Caption 1 of 24 Photos: Euro 2016 draw: 24 teams await fate There were wild celebrations in the state of Kosovo after Albania secured a spot at a major football tournament for the first time. Albania endured a rollercoaster route to Euro 2016 -- including two politically-charged games against rival Serbia. One had to be abandoned because a drone was flown over Belgrade's Partizan Stadium, causing a brawl among the players and a pitch invasion. Hide Caption 2 of 24 Photos: Euro 2016 draw: 24 teams await fate Switzerland automatically qualified behind England in Group E, even though it lost its first two games of the campaign. Many of the squad can trace their roots back to Bosnia or Kosovo, including Xherdan Shaqiri (pictured). The Swiss co-hosted the 2008 tournament with Austria, but failed to make it out of the group stages, as the national team did in its previous two appearances. Hide Caption 3 of 24 Photos: Euro 2016 draw: 24 teams await fate England became only the sixth team to win all of its Euro qualifying games. Roy Hodgson's team was the first to book its place at next year's tournament, and won all 10 qualifiers. Hide Caption 4 of 24 Photos: Euro 2016 draw: 24 teams await fate Drawn in a group with European heavyweights such as Turkey and the Netherlands, Iceland guaranteed its spot in France with two games to spare. The football minnow is the smallest country to ever qualify for the European Championship. Hide Caption 5 of 24 Photos: Euro 2016 draw: 24 teams await fate The Czech Republic, which topped Iceland's group, has qualified for every Euro tournament since 1996 -- where it lost 2-1 in the final to Germany at Wembley Stadium. Hide Caption 6 of 24 Photos: Euro 2016 draw: 24 teams await fate Turkey earned its nickname of "The Comeback Kings" in qualifying for Euro 2016 -- it only had one point after the opening three matches. The Turks reached France thanks to being the best third-placed team after beating Iceland 1-0 in the final round. Hide Caption 7 of 24 Photos: Euro 2016 draw: 24 teams await fate Belgium secured automatic qualification with a game to spare, and will be one of the teams to watch at the tournament. The 2014 World Cup quarterfinalist's squad contains many English Premier League stars -- including Eden Hazard, who was The Red Devils' joint top scorer with five goals. Hide Caption 8 of 24 Photos: Euro 2016 draw: 24 teams await fate Gareth Bale will lead Wales to its first major tournament since the 1958 World Cup. The "Red Dragons" conceded just four goals in nine matches, finishing second behind Belgium. Hide Caption 9 of 24 Photos: Euro 2016 draw: 24 teams await fate Spain is looking to win an unprecedented third European title in a row, having won the competition in 2008 and 2012. The 2010 World Cup winners topped Group C with ease -- winning nine games in row. Hide Caption 10 of 24 Photos: Euro 2016 draw: 24 teams await fate Slovakia reached its first major tournament with a 4-2 victory over Luxembourg. Its first win in four matches meant Ukraine finished third in Group C and will face a playoff. Hide Caption 11 of 24 Photos: Euro 2016 draw: 24 teams await fate Germany reached Euro 2016 with relative ease, despite losses to Republic of Ireland and Poland. Thomas Mueller top-scored for the world champions with nine goals. The Germans were runners-up in 2008 and third in 2012. Hide Caption 12 of 24 Photos: Euro 2016 draw: 24 teams await fate An inspired Robert Lewandowski helped Poland book its place at Euro 2016. The forward's record-equaling 13th goal of the campaign secured his country second place in Group D. Poland will be hoping Lewandowski can propel it out of the group stage for the first time in its history. The Bayern Munich striker has smashed 25 goals for club and country this season. Hide Caption 13 of 24 Photos: Euro 2016 draw: 24 teams await fate Northern Ireland reached its first major tournament in 30 years, topping Group F by one point from Romania. Hide Caption 14 of 24 Photos: Euro 2016 draw: 24 teams await fate Romania will make its fifth appearance in a European Championship thanks to five wins and five draws in Group F. Hide Caption 15 of 24 Photos: Euro 2016 draw: 24 teams await fate Austria played in its first European Championship in 2008 as co-host with Switzerland. It ended prematurely, however, as Austria failed to make it beyond the group stage. This time Austria topped Group G in qualifying, winning nine games and drawing once. Hide Caption 16 of 24 Photos: Euro 2016 draw: 24 teams await fate Leonid Slutskiy was key to turning around Russia's fortunes -- he was put in temporary charge of a side which was four points adrift of second-placed Sweden in Group G when Fabio Capello departed. But four wins on the bounce helped the country to reach its fifth European Championship. Hide Caption 17 of 24 Photos: Euro 2016 draw: 24 teams await fate World Cup winner Andrea Pirlo will be hoping to add the Euros to his list of honors next year after returning to the national team for the qualifiers. The veteran Italy midfielder suffered defeat in the 2012 final against Spain, a crushing 4-0 reverse. The Azzurri, unbeaten in topping Group H this time, also finished runners-up in 2000. Hide Caption 18 of 24 Photos: Euro 2016 draw: 24 teams await fate Croatia leapfrogged Norway to second place in Group H thanks to Ivan Perišić (L) hitting the only goal against Malta in the last round. It will be Croatia's third successive appearance at the finals. Hide Caption 19 of 24 Photos: Euro 2016 draw: 24 teams await fate Portugal captain Cristiano Ronaldo's five goals helped his country top Group I. The 2004 finalist won seven games in a row, after losing its opening match to Albania. Third-placed Denmark went into the playoffs. Hide Caption 20 of 24 Photos: Euro 2016 draw: 24 teams await fate Four sides booked their place at Euro 2016 after winning a two-legged play-off tie.



Ukraine will be in France next year after they drew 1-1 with Slovenia -- enough for a 3-1 aggregate victory. They co-hosted the 2012 edition with Poiand, where they failed to progress to the quarterfinals. Hide Caption 21 of 24 Photos: Euro 2016 draw: 24 teams await fate Zlatan Ibrahimovic prolonged his international career after securing Sweden a Euro finals place with a 4-3 aggregate win over neighbors Denmark. The Swedes -- finalists at the 1958 world cup -- will partake in their fifth successive European Championship, their sixth in total. Hide Caption 22 of 24 Photos: Euro 2016 draw: 24 teams await fate Republic of Ireland fans can start to plan their trip to France after a Jon Walters brace ended Bosnia-Herzegovina's hopes of reaching Euro 2016. The 3-1 aggregate Irish victory. came six years to the week after their hearts were broken by an unnoticed Thierry Henry handball -- which cost them a spot at the 2010 world cup. Hide Caption 23 of 24 Photos: Euro 2016 draw: 24 teams await fate Thirty years since their last major tournament, Hungary are bound for the finals after defeating Norway 3-1 on aggregate -- their first Euros since 1972. The Magyars had three different coaches over the course of the qualifying campaign. Hide Caption 24 of 24

An early test of security measures -- at the French Cup Final between Paris St. Germain and Olympique de Marseille last month -- was not a great success.

Despite heightened security, some fans were able to smuggle in and let off firecrackers and smoke bombs. Recriminations involving private security firms and the police followed.

Fan zones for Euro 2016, where supporters will be able to watch games on giant outdoor screens, will also need to be secured. The largest, at the foot of the Eiffel Tower, is expected to handle 90,000 fans.

Metal detectors, video surveillance, sniffer dogs and a large police presence are among the security precautions for the zones; fans will not be allowed to bring in large bags.

Terrorist prize

The lure of an event like Euro 2016 for ISIS or al Qaeda is considerable, with billions of people around the globe watching live television coverage of the games and fan zones.

ISIS would regard an attack anywhere in France during Euro 2016 or the Tour de France cycling event in July as a success.

In its latest travel warning, the U.S. State Department noted that "Euro Cup Stadiums, fan zones and unaffiliated entertainment venues broadcasting the tournaments in France represent potential targets for terrorists."

Patrick Calvar, head of France's internal security, said: "We risk being confronted by a new form of attack -- a terrorist campaign characterized by the placing of explosive devices in places where there are large crowds and repeating this type of action to create a climate of panic."

Intense security measures, including body searches and ID checks, and reducing the number of access points to stadia, may lead to large concentrations of fans trying to get into games -- an inviting target for terrorist bombings.

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The fact that several of the competing nations at Euro 2016 are part of the anti-ISIS coalition is an added incentive to the group.

In a recent audio message, ISIS spokesman and leading ideologue, Mohammed al Adnani, called on Muslims in Europe to step up attacks.

"The smallest action you carry out in their homelands is better and more favored by us from the biggest of actions in our midst; it is more successful for us and more brutalizing to them," he said.

Adnani added that civilians were a legitimate target. "Know that targeting so-called civilians is more beloved to us...more brutalizing and painful to them," he said.

According to Mohamed Abrini, who was arrested after the Brussels attacks and is also suspected of involvement in last November's Paris attacks, Euro 2016 was the ultimate target of the cell.

Belgian investigators believe that only when key members of the group were arrested, did others change their plans and carry out the March attacks in the Belgian capital.

The great unknown is whether other ISIS members who have returned to Europe have been able to organize and plan further attacks without being tracked.

According to French intelligence officials, more than 2,000 French citizens or residents are known to have links to jihadist networks in Syria and Iraq.

What Paris can learn from London 2012 Olympics

The man tasked with preventing terror attacks at the London Olympics in 2012, Richard Walton, says an aggressive, multi-layered approach is essential.

Walton, then head of the Counter Terrorism Command of the London Metropolitan Police, says every scenario was planned for -- including terrorists flying into the Olympic stadium using a microlight, a drone armed with explosives ﬂying into an open venue, and even a speedboat being used to target Olympic sites on the River Thames.

UK police also took an aggressive approach to possible suspects -- by arresting them for minor criminal offenses.

Writing in the new edition of the Combating Terrorism Center's monthly publication "Sentinel," Walton says "approximately 40% of the several thousand Islamist extremists across the country were committing low-level criminality with offenses that included beneﬁt fraud, disqualiﬁed driving, and even drug crimes."

Venues were also in lockdown weeks before events and after they had been subjected to an inch-by-inch security sweep. Access was then strictly limited through airport-style search regimes.

Photos: David Beckham through the years Photos: David Beckham through the years David Beckham through the years – David Beckham is a man of many talents. Not only is he one of the most famous names in sports, but he's also one heck of a model. Tommy Hilfiger has now recognized the 38-year-old former soccer player as the No. 1 underwear model of the century . It's just one of several career highs for Beckham, seen here modeling Emporio Armani underwear in a 2009-2010 ad campaign. Hide Caption 1 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham makes his England debut at a World Cup qualifying match against Moldova in 1996. Hide Caption 2 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham celebrates his goal against Colombia in the 1998 World Cup. Hide Caption 3 of 23 Photos: David Beckham through the years David Beckham through the years – As a player on Manchester United, Beckham cools down during the FA Charity Shield match against Arsenal in 1998. Hide Caption 4 of 23 Photos: David Beckham through the years David Beckham through the years – At the 1998 World Cup, in a second-round match against Argentina, Beckham was sent off for kicking out at Diego Simeone. England lost the match on penalties and was eliminated, with Beckham becoming a hate figure for some fans. Hide Caption 5 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham poses after a news conference in Awaji-shima Island, Japan, in 2002. Hide Caption 6 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham poses with Beyonce, left, and Jennifer Lopez in Madrid during a presentation of the new Pepsi "Samourai" in 2004. Hide Caption 7 of 23 Photos: David Beckham through the years A name brand – Beckham acts as England's captain during the 2004 European Championships in Portugal. Hide Caption 8 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham waves after a La Liga match between Real Madrid and Deportivo La Coruna in 2007. Hide Caption 9 of 23 Photos: David Beckham through the years David Beckham through the years – The midfielder celebrates with his sons in 2007 after Real Madrid won the Spanish League title by beating Mallorca. Hide Caption 10 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham makes an appearance to promote his fragrance "David Beckham Intimately Night" in Sydney in 2007. Hide Caption 11 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham reveals his new No. 32 jersey after his loan move to AC Milan in 2008. Hide Caption 12 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham controls the ball during a 2010 World Cup qualifier. Hide Caption 13 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham, during his time with the Los Angeles Galaxy, walks toward the line judge to have a chat during Game 1 of the MLS Western Conference semifinals in 2009. Hide Caption 14 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham arrives at Sydney International Airport in 2010. Hide Caption 15 of 23 Photos: David Beckham through the years David Beckham through the years – David and his wife, Victoria, arrive at the wedding of Prince William and Kate Middleton at Westminster Abbey in 2011. Hide Caption 16 of 23 Photos: David Beckham through the years David Beckham through the years – The Beckhams attend the Vanity Fair Oscar Party in West Hollywood, California, in 2012. Hide Caption 17 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham celebrated his second MLS Cup in December 2012 when he decided to leave with a year left on his contract and seek one final challenge in Europe. Hide Caption 18 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham passes under London's Tower Bridge in a speedboat carrying the Olympic Torch in 2012. Hide Caption 19 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham poses with Paris Saint-Germain President Nasser Al-Khelaifi, left, and PSG sports director Leonardo during a news conference announcing his new gig in January 2013. Hide Caption 20 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham waves after PSG played Brest in his final home match in May. Beckham had signed on with the team just a few months prior to his retirement. Hide Caption 21 of 23 Photos: David Beckham through the years David Beckham through the years – Beckham and his daughter, Harper, make their way through a crowd in New York in February. Harper, Beckham's fourth child, was born in 2011. Hide Caption 22 of 23 Photos: David Beckham through the years David Beckham through the years – Since retiring from soccer, Beckham has tried his hand at acting. It was announced in March that he will appear in a special edition of the UK classic sitcom, "Only Fools and Horses, " to raise money for a good cause. Hide Caption 23 of 23

"Our largely unarmed police presence at the London Olympics created a relaxed atmosphere, and much of our armed policing response capabilities were not visible to those participating or watching the games," says Walton of London's security style.

Severe flooding in northern France and a rash of labor strikes -- with the threat of more to come -- have not helped preparations for a relaxed Euro 2016. But President Hollande says his government is determined to make Euro 2016 "a European festival, a festival of the people."