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Laurent Cipriani, Associated Press
A worker prepares booths at a polling station in Lyon, central France, Saturday, April 22, 2017. The two-round presidential election will take place on April 23 and May 7.

PARIS — Polling stations opened Saturday in France's far-flung overseas territories — one day earlier than on the mainland — for the country's unpredictable presidential election as the 11 candidates in the race observed a ban on campaigning.

France's 10 percent unemployment and the country's lackluster economy top voters' concerns as first-round ballots are cast this weekend in the most nail-biting French election in generations.

Opinion polls showed a tight race among the four top contenders vying to get the May presidential 7 runoff that will decide who becomes the next head of state. But the polls also showed that the future of France was largely in the hands of the one-in-three voters who were still undecided.

A deadly attack on police on Paris' famed Champs-Elysees Avenue clouded the last days of campaigning. Security is a prominent issue after a wave of extremist attacks on French soil, including Thursday night's attack by a gunman who killed a Paris police officer before being shot dead by security forces. The gunman had a note in his pocket praising the Islamic State group.

Political campaigning is banned beginning Saturday across France and online and several candidates canceled appearances Friday hours after the attack.

Polling centers opened in the Atlantic Ocean territories of Saint Pierre and Miquelon as well as French Guiana in South America, the Caribbean's Guadeloupe and elsewhere. Voters abroad could also cast ballots in French embassies.

Polls suggested that far-right nationalist Marine Le Pen and Emmanuel Macron, an independent centrist and former economy minister, were in the lead.

However, conservative Francois Fillon, a former prime minister whose campaign was initially derailed by corruption allegations that his wife was paid as his non-working parliamentary aide, appeared to be closing the gap, as was far-leftist candidate Jean-Luc Melenchon.

The mad-dash campaigning of the last few weeks came to an abrupt halt hours after the Champs-Elysees gun attack by 39-year-old Karim Cheurfi. Three suspects close to the attacker remain in custody, Agnes Thibault-Lecuivre of the Paris prosecutor's office said Saturday.

Le Pen and Fillon canceled their last campaign events Friday over security concerns. Macron did too, but also accused his rivals of trying to capitalize on the attack with their anti-immigration, tough-on-security messages.

On Saturday, flowers, candles and messages of solidarity with police adorned a makeshift memorial for the slain police officer, Xavier Jugele. Small groups of well-wishers paid their respects at the site of the shooting.

Some believed French stoicism would prevent a lurch to the right in the vote, despite the fact the attack dominated French newspaper and TV headlines.

"These 48 hours are not going to change everything ... terrorism is now an everyday occurrence. It's permanent, 24 hours a day. So we're not afraid. If we're believers, believers in freedom, we must live with it," said Marise Moron, a retired doctor.

Others, fearful that the far-right Le Pen has been strengthened by the instability, said they would shift their votes from fringe candidates to make sure to keep the far-right out of power.

"With an attack such as this one, I think the National Front will get a good score. Therefore, I'm going to change my intention and I'm going to cast a useful vote. Either Melenchon or Macron," said physics teacher Omar Ilys, 44.

When French voters cast their ballots for president Sunday, their choice will resonate far beyond France's borders, from Syrian battlefields to Hong Kong trading floors and the halls of the U.N. Security Council.

The election is also widely being viewed as a ballot on the future of the European Union. The far-right Le Pen and the far-left Melenchon could pull France out of the 28-nation bloc and its shared euro currency — a so-called Frexit.

A French exit could ignited a death spiral for the EU, the euro and the whole idea of European unity that was borne out of the bloodshed of World War II. France is a founding member of the EU and its main driver, along with former rival Germany.

Financial markets are already jittery over a possible Frexit, capital flight, defaults or lawsuits on bonds and contracts. Le Pen's team is downplaying apocalyptic scenarios and arguing that the euro — now used by 19 nations — is headed for a breakup eventually anyway.

If Le Pen or Melenchon win a spot in the runoff, it will be seen as a victory for the populist wave reflected by the votes for Donald Trump and Brexit — the British departure from the EU. Many French workers who have lost out by globalization are similarly fed up with establishment parties and attracted by promises of ditching the status quo.

Alternatively, if neither candidate makes it past Sunday's first round into the May 7 runoff, that's a clear message that populist nationalism is receding.

Macron and Fillon, meanwhile, are committed to European unity and would reform labor rules. Macron has framed himself as a bulwark against Trump's protectionism.

Le Pen and Melenchon blame free trade pacts for killing French jobs and want to renegotiate them.

David Keyton and Angela Charlton in Paris contributed to this report