French President Francois Hollande called for "justice" Tuesday over the alleged rape of a black youth with a police baton, appealing for calm after more than a week of riots.

An explosion at a nuclear power station in northern France on Thursday caused minor injuries but happened outside the plant's nuclear zone and posed no risk of contamination, authorities said.

Former French president Nicolas Sarkozy is to face trial on charges of illegally financing his failed 2012 re-election bid, causing more trouble for the country's rightwing Republicans party.

The prosecution claims Sarkozy spent nearly double the legal limit of 22.5 million euros ($24 million) on his lavish campaign, using false billing from a public relations firm called Bygmalion.

Far-right leader Marine Le Pen vowed Sunday she would be a president who puts France first as she formally launched a campaign echoing many of the themes that propelled Donald Trump to the White House.

Presidential candidate Emmanuel Macron, riding high in the polls, said on Saturday he could unite a divided France at a major campaign rally that drew thousands of enthralled supporters.

France's divided Socialists picked leftwinger Benoit Hamon as their presidential nominee Sunday, in the latest twist of a roller-coaster election race that has seen conservative frontrunner Francois Fillon engulfed in scandal.

Results from a Socialist primary runoff vote Sunday showed Hamon beating his centrist rival Manuel Valls, a former prime minister, with 58.88 percent of the vote in a clear victory for the left-wing of the party.

French Socialist Benoit Hamon urged voters to support his bold leftist ideas for revitalizing the country on Wednesday as his party prepares to pick its presidential candidate this weekend.

France's Socialists will offer a stark contrast in Wednesday's debate between diehard leftist Benoit Hamon and reformist ex-prime minister Manuel Valls as the two vie for the party's presidential nomination.

Seven candidates are seeking to clinch the nomination to be the ruling Socialist party candidate in France's presidential elections due in April and May this year.

European unity is the best reply to remarks by US President-elect Donald Trump that cast doubt on the continent's future, especially after Brexit, French Foreign Minister Jean-Marc Ayrault said Monday.

"The best response to the interviews given by the US president is the unity of Europeans, to come together as a bloc," Ayrault said as he went into a meeting of European Union foreign ministers.