France was on edge Saturday on the eve of its nail-biting presidential election, which will take place under heightened security after the jihadist killing of a policeman in Paris’ Champs Elysees Avenue.

Analysts say Thursday’s attack could shake up the four-way contest between far-right leader Marine Le Pen, centrist Emmanuel Macron, conservative Francois Fillon and Communist-backed firebrand Jean-Luc Melenchon.

Authorities in Paris have offered additional guards for hundreds of polling stations in the capital, which will come on top of an already major security plan across the country.

“An extra guard or reinforcement of staff will be provided to any polling station that needs it,” Paris town hall official Colombe Brossel said.

On Sunday, around 50,000 police and 7,000 soldiers will be deployed to protect voters across France.

Until now, surveys showed the French to be more concerned about jobs and the economy than terrorism or security, though analysts warned Thursday’s shooting claimed by ISIS could change that.

A note praising the terrorist group was found next to the body of 39-year-old gunman Karim Cheurfi, who shot dead an officer and wounded two others before being killed in a firefight in Champs Elysees.

The shootings followed the arrest this week of two men in Marseille on suspicion of plotting an attack around Sunday’s first-round vote.

The attack in Paris appeared a perfect fit for Le Pen, who has moved quickly to present herself as the strongest defender against radicals in a country scarred by a string of attacks that have claimed 239 lives since 2015.

The 48-year-old leader of the anti-immigration National Front (FN) called for France to “immediately” take back control of its borders from the European Union and deport all foreigners on a terror watchlist.

Prime Minister Bernard Cazeneuve accused Le Pen of attempting to make political hay out of the Champs Elysees attack, saying she was “seeking, as she does after every tragedy, to take advantage of it”.

Fillon and Macron also hastily convened televised briefings in which they vowed to protect the country.

Veteran left-winger Melenchon, 65, was the only one of the four to stick to his schedule.

Polls showed Le Pen and Macron tied on 23 percent, ahead of Melenchon with 19.5 percent and Fillon on 19 percent.

Though the race has four main candidates, there are a total of 11 contenders, most of whom are polling in the single digits.

The top two vote getters in Sunday’s poll will head to a run-off on May 7.