Islamic State militants did not shoot down a Jordanian F-16 warplane as they have claimed, the US said.
A military statement said the plane crashed in northern Syria and confirmed that a pilot was taken captive by Islamic State forces.
But evidence indicates the Islamic State "did not down the aircraft as the terrorist organisation is claiming". The statement did not cite a cause for the crash.
In the statement, General Lloyd Austin, head of US Central Command, called the Jordanians "highly respected and valued partners".
He said their pilots and crews have performed exceptionally in the US-led bombing campaign.
Mr Austin said the US will support efforts to recover the pilot and will not tolerate attempts by the Islamic State to "misrepresent or exploit this unfortunate aircraft crash for their own purposes".
A coalition official, who was not authorised to discuss the episode publicly and spoke on condition of anonymity, said the pilot was in an F-16 fighter and was able to eject.
A Jordanian official said earlier that it was believed the plane was shot down by the extremists.
The pilot's capture underscored the risks for the United States and the multiple Arab and European countries whose warplanes are participating in a bombing campaign aimed at pushing back the jihadis' control across much of Syria and Iraq.
It also posed Jordan with a nightmare scenario, though officials vowed the country would not back down in the fight against the group.
The Islamic State group is known to have stocks of Russian-made Igla anti-aircraft missiles. The shoulder-fired weapon has long been in the Syrian and Iraqi government arsenals - it was used during the 1991 Gulf War by Iraqi forces to down a British Tornado jet, for example.
More recently, militants in Chechnya have used them to down Russian helicopters.
Jordanian information minister Mohammad Momani said that the plane was believed to have been shot down.
"It is our expectation that the plane went down because of fire from the ground, but it is difficult to confirm that, with the little information we have," he said.
Activists monitoring the conflict said Islamic State group fighters shot down the warplane near the northern Syrian city of Raqqa, the group's de facto capital.
The Raqqa Media Centre published a photograph said to be of the pilot - in a white shirt, naked from the waist down and sopping wet - being pulled by gunmen out of what appeared to be a lake. Another picture shows him surrounded by more than a dozen fighters, some of them masked. The centre said IS fighters are scouring the area in case there is a second pilot.
The United States and several Arab allies have been striking the Islamic State group in Syria since September 23, and US and other international warplanes have been waging an air campaign against the extremists in Iraq for even longer. The campaign aims to push back the jihadi organisation after it took over much of Iraq and Syria and declared a "caliphate".
Saudi Arabia, Jordan, Bahrain and the United Arab Emirates are participating in the Syria strikes, with Qatari logistical support.
The pilot's capture raises a nightmare scenario for Jordan, which has been sharply criticised by militant sympathisers for its participation. IS in the past has beheaded dozens of Syrian soldiers it captured in operations around the country. The group has also beheaded three Americans and two Britons.
Mr Momani, the informational minister, vowed that "the war on terrorism will continue," saying, the fight with the extremists was "to defend the Islamic religion".
Jordan's military said in a statement that the aircraft crashed as the air force was carrying out a military mission against the Islamic State group. "The pilot was taken hostage by the Daesh terrorist organisation," it added, using the Arabic acronym for the Islamic State group.
It said IS and "those who support it" will be responsible for the safety of the pilot. It did not give the cause of the crash or identify the type of aircraft.
The Britain-based Syrian Observatory for Human Rights said it had confirmation from activists on the ground that the aircraft was shot down, either by a Russian-made anti-aircraft missile or by heavy machine gun fire.
The Raqqa Media Centre, an agency of activists that operates openly in IS-ruled areas with permission of the group, said the plane was downed near the village of Hamra Ghannam outside Raqqa. It posted photos of militants posing with shards of wreckage. It also posted a photo of the pilot's military identification card, identifying him as Mu'ath Safi Yousef al-Kaseasbeh.
The group later showed the plane's glass canopy that was taken to a Raqqa main square where it was placed on the pavement for people to watch.
In Jordan, the pilot's cousin Marwan al-Kaseasbeh confirmed that the photos are of his cousin.
Mr Momani, the information minister, identified Mr al-Kaseasbeh by name saying "he is a symbol of heroism and sacrifice."