Coalition warplanes pounded a stronghold of the Islamic State (ISIS) group in Syria Saturday amid uncertainty over the fate of a US hostage the jihadists claim was killed in an earlier raid.
The United Arab Emirates (UAE), meanwhile, said it would station a squadron of F-16 warplanes in Jordan to support it in strikes against ISIS which burned alive a captured Jordanian airman.
The parents of American Kayla Jean Mueller said they were "hopeful" she was still alive, after ISIS said she had been buried under rubble following a strike by a Jordanian warplane on their self-proclaimed capital Raqa, reports AFP.
The United States said there was no proof that the 26-year-old aid worker from Arizona had been killed.
Mueller's parents appealed to her captors to contact them and for her safe return, in a statement carried by NBC News.
"This news leaves us concerned, yet, we are still hopeful that Kayla is alive. We have sent you a private message and ask that you respond to us privately," said Carl and Marsha Mueller.
US authorities have never given figures on the number of Americans kidnapped in Syria, sticking to a policy of complete silence.
Mueller traveled to the Syrian-Turkish border in 2012 to help refugees fleeing the civil war and was captured in Aleppo after leaving a Doctors Without Borders hospital.
Continuing to pound ISIS from the air
The Syrian Observatory for Human Rights said the US-led coalition fighting ISIS bombarded the Raqa area on Saturday for a second consecutive day.
More than 30 ISIS terrorists had been killed in raids Friday around Raqa, said the Britain-based monitor.
A coalition statement said it had carried out a total of 11 air strikes against ISIS in Syria and 15 in Iraq during a 24-hour period up to Saturday morning, including in Raqa.
Jordanian state media said its warplanes had launched new anti-ISIS raids Saturday, for the third consecutive day, without saying what the targets were.
An activist in Raqa who did not want to be named said unconfirmed reports indicate Mueller had been moved recently from a women's prison in the city to an ISIS camp farther east.
The camp "has recently been the target of intense coalition raids," he said. "At the moment, we cannot confirm whether she was killed in the raids."
Jordan - still reeling from the brutal murder of pilot Maaz al-Kassasbeh - rejected the jihadists' claim that its warplanes killed Mueller, calling it an "old and sick trick" to deter coalition strikes.
ISIS said none of its fighters was wounded in the raid, and it did not publish any pictures of her body.
The Jordanian military has said its fighter jets had launched dozens of strikes since Thursday, and that it would provide details on Sunday about the targets it says it has destroyed.
Jordanian Foreign Minister Nasser Judeh told Fox news this week the air force had targeted ISIS in both Syria and Iraq.
Meanwhile Interior Minister Hussein Majali said in remarks published Saturday that the burning alive of Kassasbeh by ISIS was a "turning point" in the kingdom's fight against the terrorists.
After Kassasbeh's warplane crashed in Syria in December and following his capture by ISIS, the UAE withdrew from the US-led coalition's strike missions over fears for the safety of its pilots.
However that move was taken back, as the federation's official WAM news agency said Abu Dhabi Crown Prince Mohammed bin Zayed al-Nahayan, deputy head of the UAE armed forces, ordered the deployment of F-16s in Jordan.
"The initiative...reaffirms the UAE's unwavering and constant solidarity with Jordan and its leading role and immense sacrifices for the security and stability of the region as embodied by martyr and hero Maaz al-Kassasbeh," the agency reported.
In northern Iraq, where Kurdish forces have pushed back ISIS, the remains of 23 men from the Yazidi religious minority were found in a mass grave, an official said on Saturday, after a similar mass grave of Yazidis was found last Monday.
ISIS, a Sunni extremist group, has seized swathes of territory in Syria and Iraq and imposed strict Sharia Islamic law on the areas under its control.