France's Thatcherite candidate Francois Fillon has said 'we are at war...it's us or them' in the wake of the Champs-Elysees terror attack as voters are expected to flock to National Front leader Marine Le Pen in Sunday's presidential election.

Fillon, who penned a pre-election book called 'Beating Islamic Totalitarianism', declared that 'the fight against terrorism must be the absolute priority of the next president'.

Vowing to 'destroy Islamic State', he added: 'We are at war, there is no alternative, it's us or them.'

Following the shooting far-right candidate Le Pen called for foreign terror suspects to be expelled immediately and said it was a 'ceaseless and merciless war' against France which required 'a presidency which acts and protects us'.

She claimed the outgoing Socialist government and its right-wing predecessor had 'done everything to ensure that we lose' the fight.

The leading candidates clashed over how to keep citizens safe in the wake of the killing of a policeman by a suspected Islamist militant in an attack that rocked France's presidential election with just two days to go before voters go to the polls.

Le Pen today called for foreign terror suspects to be kicked out the country despite the fact the ISIS gunman was French

Voters could flock to far-right candidate Marine Le Pen following the latest terror attack

With the first round of voting in the two-stage election to take place on Sunday, Le seized on the Paris shooting to push her policies on national security.

Responding to that, French Prime Minister Bernard Cazeneuve, a Socialist, said Le Pen's National Front 'after each attack, seeks to exploit it and use it for purely political means.'

Experts believe the shooting last night could boost Le Pen's chances of getting elected three days before France goes to the polls.

In last night's attack a police officer was killed and two more were injured after a gunman opened fire close to the Champs-Elysees.

Le Pen today called for foreign terror suspects to be kicked out the country despite the fact the ISIS gunman was French. The 39-year-old had used the war name 'Abu Yousuf the Belgian'.

Officials confirmed the homegrown fanatic was a French national despite his nickname.

A manhunt is underway for the second suspect who travelled by train to France from Belgium.

The Champs-Elysees terror attack could boost far-right candidate Marine Le Pen's chances of getting elected, experts believe

The shooting took place just four days before the French election and experts believe it could bolster Le Pen's chances of being elected.

Le Pen has made immigration and security the core part of her campaign.

She has pledged to tighten French borders controls and build more jails, and claimed authorities were not doing enough to protect citizens from terror attacks.

More than half of police officers in France had already said they were voting for Le Pen because of her strong anti-terror stance, according to an IFOP poll.

Experts believe it could increase her chances of winning Sunday's election.

Fredrik Erixon, director at the European Centre for International Political Economy, told CNBC: '[It could lead to] a greater performance of Marine Le Pen than otherwise would have been the case.

'It's difficult to see how this attack will not play into the hands of political forces that want this campaign to be focused only on issues around migration and terrorism.'

Vishnu Varathan, senior economist at Mizuho Bank, added: 'The Paris gunman attack may well swing support in her favor; and this may not be picked up by the polls in a timely manner.'

MAIN CONTENDERS IN FRENCH PRESIDENTIAL ELECTION Emmanuel Macron A former economy minister of Francois Hollande, the 39-year-old Centrist is the front-runner in the polls. He started a political movement called 'En Marche' that he presents as neither right-wing nor left-wing. The pro-European former investment banker is expected to become France's youngest-ever president because polls suggest if he reaches the run-off on May 7 he would defeat far-right candidate Marine Le Pen. Three surveys show Macron having a slight edge over Le Pen with 23-25 per cent against 22-23 per cent. Macron is married to his former French teacher Brigitte Trogneux, 20 years his senior, and has seven step-grandchildren. Marine Le Pen Le Pen is the candidate of her far-right National Front party. Bolstered by Donald Trump's victory as well as the Brexit result, she is campaigning on an anti-immigration, anti-Islam, nationalist plaform. Following the Champs-Elyees shooting she called for foreign terror suspects to be expelled immediately and said it was a 'ceaseless and merciless war' against France which required 'a presidency which acts and protects us'. She has also pledged to beef up law and order in her manifesto, with 15,000 more police officers, deporting foreign criminals and closing extremist mosques. A study released earlier this week revealed that 51 per cent of French police officers plan to vote for Le Pen in the upcoming polls. That is more than double the number of people who are backing Macron (16.5 per cent). According to the polls, she is currently on 22/23 per cent, but she is likely to be defeated in the second round by Macron. Francois Fillon The longtime No. 2 of former president Nicolas Sarkozy, Francois Fillon was initially installed as the favourite. However his campaign has been dogged by allegations that his Welsh wife and two oldest children improperly received public funds. He said he would step aside before performing a U-turn and he has since received a last-minute boost in the polls and is currently on 20 per cent. Fillon, who penned a pre-election book called 'Beating Islamic Totalitarianism', declared that 'the fight against terrorism must be the absolute priority of the next president'. Vowing to 'destroy Islamic State', he added: 'We are at war, there is no alternative, it's us or them.' Jean-Luc Mélenchon Far-left firebrand Mélenchon the 65-year-old is running for president for the second consecutive time after finishing in fourth place five years ago with 11 per cent of the vote. This year, Melenchon's debating skills, anti-capitalist rhetoric, pugnacity and grasp of social issues have seen him surge in the campaign's closing stages, with 19 per cent in the polls. Melenchon promises to tax the rich and spend heavily, to renegotiate France's role in the 28-nation EU and international trade pacts. He also wants to get rid of what he calls the 'presidential monarchy' by giving more power to parliament, and to stop France's use of nuclear power, the source of nearly 80 per cent of the country's electricity. If Melenchon makes it to the runoff, he is projected to beat both Le Pen and Fillon by comfortable margins although he is seen losing to Macron 41 per cent to 59 per cent. Benoît Hamon Hamon is polling in a distant fifth place ahead of Sunday's first-round election and has little chance of reaching the decisive May 7 run-off - a failure that could crush his Socialist party. He wants to legalise cannabis and tax the wealth generated by robots that take the jobs of humans. Advertisement

Pictured is the suspected ISIS gunman, who has been identified as 39-year-old father Karim Cheurfi

The killing overnight of a policeman in an ISIS attack overshadowed the last day of France's presidential election campaign

The attacker emerged from a car and used an automatic weapon to shoot at officers at the centre of the Champs-Elysees

A police officer was shot dead and two more were injured by a gunman close to the Champs Elysees

In last night's attack the gunman, identified as 39-year-old Frenchman Karim Cheurfi - who was jailed for 20 years for trying to kill officers in 2001 - parked his Audi and opened fire after police stopped at a red light on the world famous avenue.

One traffic officer died instantly with a shot to the head, while the other two were hurt before Cheurfi himself was gunned down by nearby armed police.

A ricocheting bullet fired by the terrorist also wounded a female foreign tourist passing by.

French police officers and forensic teams searched a vehicle which was close to the scene on the Champs-Elysees in Paris

A police lorry seized the Audi which the attacker was driving, before he got out and shot at officers last night

A team of forensic detectives examine the Audi, which the gunman was driving. ID of Karim Cheurfi was found in the vehicle

Armed police outside a shop in central Paris after an ISIS gunman killed an officer and injured three other people

Candidates in the upcoming election have voiced their horror over the attack in Paris

MORE THAN HALF POLICE OFFICERS VOTING FOR LE PEN A study released earlier this week revealed that 51 per cent of French police officers plan to vote for Le Pen in the upcoming polls. The poll by IFOP found that 65 per cent of frontline officers would support her in the election. That is more than double the number of people who are backing her nearest rival, centrist Emmanuel Macron (16.5 per cent). Advertisement

An Elabe survey of voter intentions taken before the shooting on the Champs Elysees shopping street in central Paris showed centrist Emmanuel Macron in front and Le Pen falling further behind him.

But the latest attack in the heart of Paris could send voters flocking to Le Pen, who has pledged to beef up law and order in her manifesto, with 15,000 more police officers, deporting foreign criminals and closing extremist mosques.

Speaking today on RFI radio, she said: 'Today fundamentalist Islam is waging war and...the measures are not being taken to limit the risks.'

She said France should immediately reinstate border checks, adding 'we need a presidency which acts and protects us.'

US President Donald Trump said today it would 'have a big effect on presidential election' as the French people 'will not take much more of this'.

Macron appealed to voters to keep a cool head in the wake of the attack.

He said: 'What our attackers want is death, symbolism, to sow panic (and) to disturb a democratic process, which is the presidential election.'

He tore into Le Pen, accusing her of lying with claims that previous attacks wouldn't have happened under her watch.

'She won't be able to protect our citizens,' Macron said of Le Pen.

He added: 'There's no such thing as zero risk. Anyone who pretends (otherwise) is both irresponsible and deceitful.'

Thatcherite candidate Fillon said 'the fight for the French people's freedom and security will be mine. This must be the priority.'

He promised to boost police and military forces.

He also said that, if elected, he would launch a 'diplomatic initiative' aiming to create an international collaboration against Islamic extremists that would include all major actors, including the United States, the European Union, Russia, Iran, Turkey and the Gulf countries.

Promising an 'iron-fisted' approach, Fillon added: 'Some haven't taken the full measure of the evil.'

Socialist Benoit Hamon tweeted his 'full support' to police against terrorism.

France has been in a state of emergency since 2015 due to a spate of terror attack that have killed more than 230 people in the past two years.

The populist French candidate said the terror threat facing the country was a result of 'laxity' in a television debate tonight

Candidates cancelled or rescheduled final campaign events ahead of Sunday's first-round vote in the two-stage election.

For weeks, former banker Macron and Le Pen have been out in front but opinion polls now show there is a chance that any of the four leading candidates could reach the second-round runoff on May 7.

Though Le Pen and Macron have become frontrunners, scandal-plagued conservative Francois Fillon and far-left firebrand Jean-Luc Melenchon have closed the gap substantially in the last two weeks.

Prime Minister Cazeneuve said France had fully mobilised its security forces, including elite units, to ensure citizens' protection during the election.

Speaking after an emergency meeting of top security officials, Cazeneuve said all elite units were on top alert for the election to back up the 50,000 police already earmarked for special election duty.

In a statement, he said: 'The government is fully mobilised. Nothing must be allowed to impede the fundamental democratic process of our country.

'It falls to us not to give in to fear and intimidation and manipulation which would play into the hands of the enemy.'

Appealing for national unity and for people 'not to succumb to fear', he added: 'Barbarity and cowardice struck Paris last night.'