The US has dismissed claims that Islamic State fighters shot down a Jordanian warplane before capturing its pilot.
IS supporters claimed the plane, which was flying with US-led coalition forces, was hit by a heat-seeking missile near Raqqa city in northern Syria.
Jordan initially said the F-16 fighter was shot down during a "military mission against the hideouts of the terrorist group" - but later said it was unclear how the plane came to crash.
Now the US Central Command has said: "Evidence clearly indicates that ISIL (IS) did not down the aircraft as the terrorist organisation is claiming."
A Washington official added that the allies were investigating whether the plane suffered a mechanical fault.
UN Secretary-General Ban Ki-moon has urged IS captors to treat the pilot "in accordance with international humanitarian law".
An army statement read on Jordanian state television said: "Jordan holds the group and its supporters responsible for the safety of the pilot and his life."
IS in Raqqa published photographs on jihadist websites purporting to show its fighters holding the captured pilot and showed a military card identifying him.
Several photographs were released, including one showing the captive, wearing only a white shirt, being carried from water by four men.
Another showed him on land, surrounded by about a dozen armed men.
The images were verified by two relatives contacted by the Reuters news agency, who said they had been notified by the head of the Jordanian air force that the pilot was First Lieutenant Muath al Kasaesbeh, aged 27. The army separately confirmed his name.
A friend said Mr Kasaesbeh, who is from a prominent Jordanian family, was passionate about his mission and felt it was a religious duty to fight extremist groups such as IS that were "distorting the true spirit of Islam".
Jordan is among a number of countries that have joined the US-led alliance carrying out airstrikes against IS after the jihadis seized large areas of Syria and Iraq.
Saudi Arabia, the United Arab Emirates, Jordan and Bahrain are taking part in airstrikes alongside the US.
