The UN has urged Islamic State fighters who captured a Jordanian pilot to treat him in accordance with international humanitarian law.
The man was captured when his warplane came down in northeast Syria this morning.
He is the first captive to be taken from the US-led coalition battling the militant group.
Jordan's armed forces said one of its pilots had been captured after a coalition air raid over the province of Raqqa.
"Jordan holds the group (IS) and its supporters responsible for the safety of the pilot and his life," a statement read on state television said.
It did not say whether the plane had been shot down but said it had crashed during a Jordanian air force "military mission against the hideouts of the terrorist group".
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 verified by two relatives contacted by Reuters who said they had been notified by the head of the Jordanian air force the pilot was First Lieutenant Muathal-Kasaesbeh, aged 27.
The army separately confirmed his name.
Meanwhile the US has dismissed the claim that IS had shot down a Jordanian F-16 fighter flying with US-led coalition forces.
"Evidence clearly indicates that ISIL did not down the aircraft as the terrorist organisation is claiming," said US Central Command, the body overseeing the coalition air war over Iraq and Syria.
A friend said Lt 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.
The US-led coalition has been bombing Islamic State targets in Syria since September.
Jordan, the staunch US ally, has provided a logistics base for the US-led air campaign and is a hub for intelligence-gathering operations against the militant, a western diplomatic source said.
King Abdullah has been in the forefront of regional US allies supportive of the campaign but has said radical Sunni extremists cannot be 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 US 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.
