Beirut (AFP) - Coalition warplanes pounded the Islamic State group's self-proclaimed capital in Syria Saturday as uncertainty surrounded the fate of a US hostage the jihadists claim was killed in an earlier raid.The parents of aid worker Kayla Jean Mueller said they were "hopeful" she was still alive, after IS claimed she had been buried under rubble following a strike by a Jordanian plane on their stronghold Raqa.The United States said there was no proof that the 26-year-old 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.According to the Syrian Observatory for Human Rights, the US-led coalition fighting IS bombarded the Raqa area on Saturday for a second consecutive day.The Britain-based monitor said more than 30 IS fighters had been killed in raids Friday around Raqa.A coalition statement said it had carried out a total of 11 airstrikes against IS 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-IS raids Saturday, without saying where.An activist in Raqa who did not want to be named said he had heard unconfirmed reports that Mueller had been moved recently from a women's prison in the city to an IS camp east of the city.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."- 'Sick trick' -Jordan -- still reeling from the brutal murder of one of its pilots by IS -- rejected the jihadists' claim that its warplanes killed Mueller, calling it an "old and sick trick" to detercoalition strikes.IS said none of its fighters was wounded in the raid, and it did not publish any pictures of her body.Its claim came as Amman said its fighter jets had launched dozens of strikes Thursday against IS, widening their campaign from Syria to include targets in neighbouring Iraq.Interior Minister Hussein Majali said in remarks published Saturday that the burning alive of a Jordanian pilot by IS was a "turning point" in the kingdom's fight against extremism.US authorities have never given figures on the number of Americans kidnapped in Syria, sticking to a policy of complete silence.Mueller travelled 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.IS, a Sunni extremist group, has seized swathes of territory in Syria and Iraq and imposed an extreme interpretation of Islam on the areas under its control.In northern Iraq, where Kurdish forces have pushed back IS, the remains of 23 men from the Yazidi religious minority were found in a mass grave, an official said on Saturday.- 'Criminal propaganda' -Thousands of Jordanians marched on Friday to demand retribution against IS for the horrifying murder of pilot Maaz al-Kassasbeh.Queen Rania joined them after weekly prayers at the Al-Husseini mosque, holding a portrait of the pilot with the words "Maaz the martyr of righteousness".The kingdom's airstrikes are "the beginning of an ongoing process to eliminate" IS, Interior Minister Majali was quoted as saying by government newspaper Al-Rai."The day of the hero, martyr pilot's assassination is a turning point in Jordan's history in order to face this horrific crime that was committed by the cowardly terrorist organisation," he said.Amman's government spokesman Mohammad al-Momani dismissed the jihadists' claim of the American's death as "criminal propaganda"."They have lied that our pilot is alive and tried to negotiate claiming he is alive while they had killed him weeks before," Momani told AFP.IS had offered to spare Kassasbeh's life and to exchange Japanese hostage Kenji Goto for Iraqi militant Sajida al-Rishawi, who was on death row for her role in deadly hotel bombings in Amman in 2005.Goto was later beheaded and Jordan hanged Rishawi after IS released the video showing the murder of Kassasbeh, who was taken prisoner in December after his F-16 crashed in Syria.Jihadists have flocked to Syria during a nearly four-year-old war in which more than 210,000 people have died, according to an updated Observatory toll.Join the conversation about this story Click here to read full news..