Islamic State militants have issued a threat to President Vladimir Putin, vowing to oust him and "liberate" the volatile North Caucasus over his support of the Syrian regime.

The General Prosecutor's Office of Russia demanded that access to the address, which was posted on YouTube on Tuesday and features what jihadists say is a Russian-supplied fighter jet, be blocked.

French President Francois Hollande on Wednesday raised the prospect of a military response to the threat posed by Islamic State extremists occupying swathes of Iraq and Syria, saying it may be necessary.

"The head of state underlined the importance of a political, humanitarian and if necessary military response in accordance with international law" to fight against IS, the presidency said in a statement summing up a restricted defense meeting.

Islamic State jihadists in Iraq and Syria pose a genuine threat to the West but are "not invincible," and U.S. air strikes have exposed their weaknesses, a top U.S. intelligence official said Wednesday.

Matthew Olsen, director of the National Counter-Terrorism Center, said there is no "credible" evidence that IS fighters are plotting an imminent attack on America but acknowledged the group could eventually try to strike at the United States.

Egyptian President Abdel Fattah al-Sisi on Wednesday blamed the stalled Israeli-Palestinian peace process for fueling regional militancy, as Washington tries to shore up support to combat Islamic State jihadists.

Sisi, a former army chief who overthrew Islamist President Mohamed Morsi last year, is battling jihadist militants in the Sinai Peninsula who have killed scores of policemen and soldiers.

Hussein Khalaf, a policeman in the Iraqi town of Amerli, holds up a bunch of grapes after the end of a long jihadist siege, saying with a smile they are the first he has seen in months.

Like thousands of others in this Shiite Turkmen-majority town north of Baghdad, Khalaf was trapped by the Islamic State (IS) jihadist group until Iraqi forces and allied militiamen broke through on Sunday.

Sixteen people, among them 10 children, were killed in a government air raid in east Syria on Wednesday, a monitor said, but state media blamed the deaths on jihadist militants.

The Syrian Observatory for Human Rights, a Britain-based monitor, said an air strike hit a bus on the road between eastern Deir Ezzor province and Damascus as it passed through the Shula area.

U.S. journalist Steven Sotloff, whose videotaped murder by the jihadist Islamic State group shocked the world, also held Israeli nationality, Israeli media reported on Wednesday.

The Haaretz newspaper cited a foreign ministry spokesman as saying that Sotloff, 31, held dual citizenship, although the ministry made no immediate comment when contacted by AFP.

An Egyptian policeman was shot dead and two colleagues were wounded in attacks in the restive Sinai Peninsula on Wednesday, security officials said, a day after a bomb killed 11 policemen.

Assailants in a car gunned down a police sergeant in the North Sinai town of El-Arish, the officials said.

A senior army intelligence official has admitted that Israel underestimated the tenacity of Gaza militants and did not expect a 50-day conflict to last so long, but he insisted they were soundly beaten.

Yemeni Shiite rebels and activists took to the streets of Sanaa Wednesday to reject a presidential overture to replace the government and reduce a disputed fuel price hike.

Faced with increased pressure from the Shiite rebels, who are also known as Huthis, and a deepening political crisis, President Abdrabuh Mansur Hadi announced the measures on Tuesday.