The United States and its Arab allies unleashed deadly bomb and missile strikes on jihadists in Syria on Tuesday, opening a new front in the battle against the Islamic State group.

Dozens of IS and Al-Qaida militants were reported to have been killed in the raids, which Washington said had partly targeted extremists plotting an "imminent attack" against the West.

An Algerian militant group said it has kidnapped a Frenchman and threatened to execute him unless Paris halts air strikes on Islamic State jihadists in Iraq, in a YouTube video posted Monday.

Jund al-Khilifa, which has pledged allegiance to IS, said it carried out Sunday's kidnapping in a mountainous region of eastern Algeria where al-Qaida is active.

France on Monday urged nationals living in or traveling to some 30 countries to exercise "utmost caution" after the Islamic State group called for Muslims to kill civilians whose governments were acting against the jihadists.

The foreign ministry said it had sent a warning note to its embassies "in around 30 countries" in Africa and the Middle East.

The Islamic State group called on Muslims to kill citizens of all countries taking part in the U.S.-led anti-jihadist coalition by any available means, in a statement posted online Monday.

"If you can kill a disbelieving American or European -- especially the spiteful and filthy French -- or an Australian, or a Canadian or any other disbeliever... including the citizens of the countries that entered into a coalition against the Islamic State, then rely upon Allah, and kill him," said Abu Mohammed al-Adnani, the group's spokesman.

French flag carrier Air France on Monday offered to freeze the expansion of its low-cost operation in a bid to end the longest strike at the airline since 1998.

As the strike entered its second week, management said it would halt the development of its leisure subsidiary Transavia until December, unions said, raising hopes of an end to the crisis.

U.S. Secretary of State John Kerry on Sunday voiced hope a long-delayed U.S.-Afghan security deal governing the presence of American troops in the country beyond 2014 may be signed shortly.

The bilateral security deal (BSA) was supposed to have been sealed by late last year, but at the last minute outgoing Afghan President Hamid Karzai refused to sign, saying he believed it was up to his successor.

"The match has begun," France's popular opposition politician Alain Juppe said Sunday after his rival and ex-president Nicolas Sarkozy announced his return to the cutthroat political arena.

Both center-right heavyweights, with their sights on 2017 presidential elections, are keen to restore the image of their UMP party, hampered by in-fighting and scandals from mounting a credible fight against the deeply unpopular Socialist government.

Former French president Nicolas Sarkozy Friday announced his return to politics in a statement on his Facebook page, vowing to offer a "new political choice" to disenchanted French voters.

"I am a candidate to be president of my political family," the conservative UMP party, said Sarkozy, putting an end to months of speculation that he would return to the political scene.

France carried out its first air strike against the Islamic State group in Iraq Friday, boosting U.S.-led efforts to unite the world against the growing threat posed by the jihadists.

More than a decade after Paris famously refused to back the invasion of Iraq, France became the first nation to join the U.S. campaign of air strikes in the war-torn country.

President Francois Hollande announced Thursday that France has decided to conduct air strikes in Iraq, where militants from the Islamic State group have terrorized large parts of the population.

France will join the United States in providing what Hollande called "aerial support" for the Iraqi army in fighting jihadists who have taken over nearly half of the violence-ridden country.