(CNN) The scenes were horrific: Vacationers snapped from their naps by the sound of gunfire. The screams of the injured. Blood on the beach.

Yet it was just one of three terrorist attacks on three continents that followed one another in frightening succession last week. While it is not yet known whether the attacks were linked, they have left officials in numerous countries concerned about how to keep their citizens safe.

A series of terrifying attacks

Police secure the entrance of the factory on June 26.

Police secure the entrance of the factory on June 26.

The June 26 attack also involved at least one explosion, officials said.

The June 26 attack also involved at least one explosion, officials said.

Police block the area where the attack took place on June 26.

Police block the area where the attack took place on June 26.

Investigators work at the enclosed area where a decapitated body was discovered at the Saint-Quentin-Fallavier factory on June 26. The severed head was found with a message, Hollande said.

Investigators work at the enclosed area where a decapitated body was discovered at the Saint-Quentin-Fallavier factory on June 26. The severed head was found with a message, Hollande said.

French President François Hollande, at a June 26 news conference in Brussels, Belgium, called the crime a "pure terrorist attack."

French President François Hollande, at a June 26 news conference in Brussels, Belgium, called the crime a "pure terrorist attack."

Police and firefighters gather at the entrance of Air Products & Chemicals, a gas factory near Lyon, France, on Friday, June 26, after a terror attack. One person has been beheaded and two people injured, French President François Hollande said Friday. A suspect has been arrested, he said.

Police and firefighters gather at the entrance of Air Products & Chemicals, a gas factory near Lyon, France, on Friday, June 26, after a terror attack. One person has been beheaded and two people injured, French President François Hollande said Friday. A suspect has been arrested, he said.

On Friday morning, European time, the head of the decapitated manager of a transportation company was found hanging from a fence near Lyon, in southern France, along with two banners said to bear Islamic writing. The attack, at a U.S.-owned factory, began when a delivery van, allegedly driven by Yassin Salhi, entered the facility, according to Paris Prosecutor Francois Molins, whose office handles anti-terrorism cases throughout France.

-- Not long after that, a bomb ripped through Al-Sadiq mosque in Kuwait's capital during Friday prayers -- a time when mosques are packed with worshippers. At least 27 people were killed. ISIS has posted a video of a man it claims is the suicide bomber, identifying him as Abu Suleiman al-Muwahid -- presumably a nom de guerre.

-- Then came news that a gunman had sprayed a tourist beach in Sousse, Tunisia, with bullets, killing at least 38 people and injuring at least 39 others. ISIS has claimed responsibility for that attack, as well, though this claim may be more tenuous.

The attacker, identified by authorities as 24-year-old Saif Al-Deen Al Rezgui, was shot dead by police Friday outside the hotel.

Tunisian Interior Minister Najem Gharsalli said Monday that the country had made its first arrests in connection with Friday's attack.

"We have started by arresting a first group, the important part of the network that was behind this terrorist criminal," Gharsalli said. He made the announcement during a joint press conference with his German, French and British counterparts in Sousse.

Was Tunisian attacker associated with terror group?

Tunisian Prime Minister Habib Essid told CNN's Becky Anderson Monday that there was little information on whether Al Rezgui was involved in an organized terror group.

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Studying at university, the gunman was involved in a few organizations on campus that are being investigated for ties to the attack.

"We cannot establish at this moment, but there is some information that he belonged to an organization," he said, describing a mosque that may have influenced Al Rezgui's thinking.

A spokesman for Tunisia's Interior Ministry told CNN that Al Rezgui indeed had a connection to a Libyan terrorist organization. However, Mohammed Ali Aroui said it was unclear whether the gunman had a link to the Ansar Al-Sharia militant group or ISIS in Libya.

Police have also not yet confirmed whether Al Rezgui had ever traveled to Libya, he added.

Al Rezgui had a Tunisian passport but it's unclear whether he traveled out of the country for training with a militant group. Essid noted that sometimes people illegally cross the border between Libya and Tunisia.

Essid added that Al Rezgui could have used social media and online tools to prepare him for attack.

With Tunisia being such a popular tourist destination, the massacre has brought a wave of devastation over the economy.

"It's a heavy damage because the sector is drowning. We must do everything to save the situation," Essid said.

A terrible toll for Britain

For Britain, the news coming from Tunisia is likely to get worse.

A spokeswoman for British Prime Minister David Cameron said Monday that 18 British nationals were known to have been killed during the attack Friday. But the spokeswoman said the grim toll would, in all probability, increase to about 30.

The interior ministers of Britain, Germany and France gathered Monday in Tunisia to show their solidarity with Tunisian authorities and to vow to defeat the terrorists.

Photos: Terrorist attack in Tunisia Photos: Terrorist attack in Tunisia People lay flowers on the beach in front of Hotel Riu Imperial Marhaba, in the coastal city of Sousse, Tunisia, on Saturday, June 27. Gunmen killed at least 38 people at site , the same day terrorists lashed out brutally in France and bombed a mosque in Kuwait. Hide Caption 1 of 14 Photos: Terrorist attack in Tunisia Tunisian police patrol the beach in front of the Riu Imperial Marhaba Hotel on June 27. Hide Caption 2 of 14 Photos: Terrorist attack in Tunisia A Tunisian forensics expert inspects the beach on June 27. Hide Caption 3 of 14 Photos: Terrorist attack in Tunisia A young woman lays flowers at the scene of a shooting on June 27. Hide Caption 4 of 14 Photos: Terrorist attack in Tunisia Tourists leave Tunisia at the Enfidha International airport a day after the attack. Hide Caption 5 of 14 Photos: Terrorist attack in Tunisia Tunisian security forces stand in front of Hotel Riu Imperial Marhaba on Friday, June 26. Hide Caption 6 of 14 Photos: Terrorist attack in Tunisia Tunisian security forces evacuate the hotel. At least one gunman was reportedly killed, according to the state-run TAP news agency. Hide Caption 7 of 14 Photos: Terrorist attack in Tunisia On its website, Hotel Riu Imperial Marhaba is described as an all-inclusive hotel with views of Port El Kantaoui. Hide Caption 8 of 14 Photos: Terrorist attack in Tunisia Tunisian President Beji Caid Essebsi, third from right, arrives at the resort with Prime Minister Habib Essid, third from left, and Interior Minister Mohamed Najem Gharsalli, far left. Hide Caption 9 of 14 Photos: Terrorist attack in Tunisia Hide Caption 10 of 14 Photos: Terrorist attack in Tunisia A medic stands next to the body of a tourist. Hide Caption 11 of 14 Photos: Terrorist attack in Tunisia Dead bodies are seen on the beach. Hide Caption 12 of 14 Photos: Terrorist attack in Tunisia A Tunisian security member stands next to a swimming pool at the hotel. Hide Caption 13 of 14 Photos: Terrorist attack in Tunisia Tunisian medics stand near a tourist's body. Hide Caption 14 of 14

Theresa May, Britain's home secretary, said all were united in their determination "to fight against this perverted ideology that is causing this death and destruction."

The ministers said their meeting would be followed by other meetings of experts from their various countries.

Gharsalli, the Tunisian interior minister, said his government might close mosques "that use an anti-democratic language and that use a language of hatred."

In Britain, Cameron told the House of Commons that a major counterterrorism training exercise would take place in London over the next few days. The exercises will involve security and emergency services, he said.

A national minute of silence -- a rare event in Britain -- will be held this Friday, a week after the Tunisia attack occurred, Cameron said.