Three years after France's upper house Senate made its first ever swing to the left, the right has clawed back a majority, with the far-right National Front winning seats for the first time.

The results were a new setback for beleaguered Socialist President Francois Hollande.

Three Frenchmen arrested in Turkey after traveling to Syria were charged Saturday with planning terrorist acts, one of their lawyers said. 

The men, who were the subject of a high-profile judicial bungle this week after their arrest in Turkey, were being charged with "criminal association with the aim of planning terrorist acts", lawyer Pierre Dunac told Agence France-Presse.

A young man was detained Friday at an airport in southern France as he returned from Iraqi or Syrian "combat zones" via Turkey, a source close to the case said.

Aged "less than 20", the French national was on a wanted list and was immediately taken in for questioning by intelligence services after his arrest at Nice airport, the source added, without giving any further details as to whether the man is a suspected jihadist.

The French interior minister on Friday held talks with his Turkish counterpart aimed at improving intelligence and security communications after an embarrassing bungle allowed three suspected jihadists who fought in Syria to walk free.

Bernard Cazeneuve met Turkish Interior Minister Efkan Ala days after a communications breakdown between the two sides allowed the three suspects to saunter out of a French airport unhindered after being deported from Turkey.

Top U.S. diplomat John Kerry was to meet with his Iranian counterpart Friday for a second time in two days, amid reports that tough talks on reining in Tehran's nuclear program have become deadlocked.

"At this time as I speak, there is no significant progress," French Foreign Minister Laurent Fabius said of the latest round discussions.

Hundreds of people gathered in Paris Friday answering a call by Muslim leaders to denounce the "barbarism" of Islamic State militants, as flags across France flew at half mast after the beheading of a French national.

Imams and ordinary Muslims have rallied to condemn the execution of 55-year-old mountaineer Herve Gourdel this week by militants in Algeria with ties to the IS jihadists, as the country mourned the brutal murder.

Paris said Thursday it had widened its vigilance alert for nationals abroad from 31 to 40 countries including Asian nations, after a French hostage was beheaded in Algeria by jihadists linked to the Islamic State group.

"We have extended the call (for vigilance) to some 10 more countries," Didier Le Bret, head of the foreign ministry's crisis center, told Agence France-Presse, adding Muslim countries in Asia were now included.

France launched a fresh round of air strikes in Iraq Thursday and pledged more support for Syrian opposition forces as it upped its fight against Islamic State jihadists after the beheading of hostage Herve Gourdel.

President Francois Hollande pledged "determination, composure and vigilance" in the face of threats issued by IS militants sowing terror in Iraq and Syria, and announced flags nationwide would be flown at half-mast for three days from Friday to mourn the mountaineer's loss.

France said Thursday it will increase support to Syrian opposition forces fighting Islamic State jihadists, after the execution of a citizen in Algeria by militants tied to the group.

Security will be reinforced across France in public spaces and on public transport, after threats made by IS against French citizens, according to a statement from President Francois Hollande's office following emergency defense talks.

Islamic State jihadists have seized and set fire to a cement factory in Syria owned by French construction materials giant Lafarge, causing damage to the facility, a monitor said Thursday.

"While advancing on the Kurdish town of Ain al-Arab (Kobane in Kurdish) near the Turkish border, they seized the Lafarge factory and burnt down part of it," said Rami Abdel Rahman of the Syrian Observatory for Human Rights.