Jordan's armed forces said one of its pilots had been captured after a coalition air raid over the province of Raqqa. There were contradictory accounts as to whether his aircraft had been shot down or not.

"Jordan holds the group (IS) and its supporters responsible for the safety of the pilot and his life," said a statement read out on state television.

It said the F-16 warplane had crashed during a Jordanian air force "military mission against the hideouts of the terrorist group".

Jordan's government spokesman Mohammad Al-Momani told satellite TV station Al Hadath the jet fighter "was shot at from the ground by rocket missiles and was brought down" and that an attempt to rescue the pilot before he was captured failed. He did not elaborate.

But Momani later told Reuters that new assessments showed there was no indication the plane had been shot at by the militants.

"We initially thought the plane might have been shot at, but we cannot confirm this now," he added.

An official source said King Abdullah met top commanders in Jordanian military headquarters, where a round-the-clock operations room had been set up after the pilot's capture.

The U.S. military's Central Command said evidence showed Islamic State did not shoot down the aircraft. It did not disclose the nature of that evidence.

The head of Central Command, General Lloyd Austin, said the United States would "support efforts to ensure his safe recovery and will not tolerate ISIL's attempts to misrepresent or exploit this unfortunate aircraft crash for their own purposes".

One U.S. official, speaking on condition of anonymity, said U.S. aircraft took to the air once the Jordanian jet crashed but the pilot was picked up before any rescue attempt could be launched.

PICTURES OF PILOT

The Jordanian statement described Islamic State as a "group that does not conceal its terrorist plots, committing many criminal acts from wanton destruction to killing innocent Muslims and non-Muslims in Syria and Iraq".

Islamic State social media published pictures appearing to show the pilot being held by the group's fighters and images of what they said was his Jordanian military ID card.

The images were later verified by relatives contacted by Reuters who said they had been notified by the head of the Jordanian air force the pilot was First Lieutenant Muath al-Kasaesbeh, aged 27. The army separately confirmed his name.

His father, Safi Yousef, appealed to the captors to show mercy and release his son, whom relatives say is a pious Muslim.

A friend said Kasaesbeh, who is from a prominent Jordanian family, was fervent in his commitment to his mission and felt it was a religious duty to fight extremist groups such as Islamic State that were "distorting the true spirit of Islam".

One of the published images showed the pilot, wearing a white shirt, being led out of water by armed fighters. Another showed him on land surrounded by at least a dozen fighters in military fatigues and equipped with assault rifles.

Jordan is one of the countries participating in the U.S.-led coalition which has been bombing Islamic State targets in Syria since September.

The staunch U.S. ally has provided a logistics base for the U.S.-led air campaign and is a hub for intelligence-gathering operations against the jihadists, a western diplomatic source said.

A U.S. National Security Council spokeswoman said the administration was in close touch with the Jordanian government and "our thoughts and prayers are with the pilot, his family, and our partners in the Jordanian Armed Forces".

King Abdullah has been in the forefront of regional U.S. allies supportive of the campaign but has said radical Sunni extremists cannot defeated by military means alone and their ideology must be confronted with reason.

Saudi Arabia, Qatar, Bahrain and the United Arab Emirates have also joined or supported the strikes against Islamic State targets in Syria, according to U.S. Central Command.

Raqqa province, which borders Turkey, is almost entirely under the control of Islamic State fighters.

Boosted by arms seized in Iraq, the group evicted most rival rebels from the province earlier this year and took control of a string of government military bases over the summer, including an air base.

The United States is also bombing Islamic State targets in Iraq, where the group has seized swathes of territory.