Kayla Mueller, the U.S. aid worker held by Islamic State militants in Syria, has died. Her parents confirmed her death. President Obama said the United States will “find and bring to justice the terrorists who are responsible.” (Reuters)

The U.S. government has confirmed that Kayla Mueller, a 26-year-old American woman held hostage by the Islamic State in Syria, was killed, reaching that conclusion after the group sent pictures of her body to her family.

“We are heartbroken to share that we’ve received confirmation that Kayla Jean Mueller has lost her life,” her parents said in a statement Tuesday. “Kayla was a compassionate and devoted humanitarian. She dedicated the whole of her young life to helping those in need of freedom, justice, and peace.”

[Read: Mueller’s handwritten letter to her family while she was in captivity]

In a statement, President Obama said that “it is with profound sadness that we have learned of the death of Kayla Jean Mueller. On behalf of the American people, Michelle and I convey our deepest condolences to Kayla’s family — her parents, Marsha and Carl, and her brother Eric and his family — and all of those who loved Kayla dearly. At this time of unimaginable suffering, the country shares in their grief.”

In an emotional news conference Tuesday in her home town of Prescott, Ariz., friends and relatives of Kayla Mueller hailed her passion for helping those in need and her free spirit. The Rev. Kathleen Day, who headed a campus ministry that Mueller joined at Northern Arizona University, recalled that she wrote in a letter from captivity that she tried to teach crafts to her guards, including how to make origami peace cranes.

Friends and family of Kayla Mueller mourned her death on Tuesday after receiving confirmation that the U.S. hostage being held in Syria by the Islamic State had been killed after months in captivity. (Reuters)

“We just delight in that,” Day said, “that Kayla remained Kayla. She said she found freedom even in captivity.”

The news conference shed no light on how Mueller died.

The Islamic State announced Friday that Mueller was killed when a Jordanian fighter jet bombed the building where she was being held in the north-central Syrian city of Raqqa, the group’s de facto capital. It was the first time the Islamic State, a radical al-Qaeda offshoot, had acknowledged publicly that it was holding the young woman.

Mueller’s family received an e-mail over the weekend with “additional information about her death,” White House press secretary Josh Earnest said. “That information was shared with the intelligence community,” which “concluded that Kayla has, in fact, died.”

The information available to intelligence officials, Earnest said, “did not allow them to arrive at a conclusion about her precise cause of death” or when it occurred. He and other U.S. officials said they would not provide details of the pictures her family received, “out of respect for the family.”

U.S. officials have expressed strong skepticism that she was killed in an airstrike. Earnest repeated earlier Jordanian statements that the target hit in the Friday strike by the Jordanian air force — a building that militants showed in photographs posted online at the time they announced Mueller’s death — was a “weapons compound” near Raqqa that had also been hit in earlier strikes.

“The information that we have, because this airstrike was coordinated with the United States military, is that there was no evidence of civilians in the target area prior to the coalition airstrike taking place,” Earnest said.

President Obama says his immediate reaction was ‘heartbreak’ over the death of U.S. hostage Kayla Mueller, but defends U.S. policy not to pay ransoms to terrorist groups like the Islamic State. (Reuters)

[Related: Islamic State claims American hostage killed in bombing in Syria]

Jordan’s information minister, Mohammad al-Momani, said in a statement: “Jordan strongly condemns the brutal killing of the American hostage. We express our sincere grief and are deeply angered by this barbaric brutality. Countries around the world must continue to work together to fight and defeat this evil.”

The Jordanian government has denied that its airstrikes killed Mueller.

Mueller was abducted in August 2013 after leaving a hospital in the Syrian city of Aleppo. She had traveled to the region in late 2012 to help refugees trying to escape the civil war in Syria.

Mueller is the fourth American since August to die while being held hostage by the Islamic State. The group is still holding a British journalist.

Mueller’s parents had held out hope that their daughter was alive, issuing a statement Friday to her captors.

“This news leaves us concerned, yet, we are still hopeful that Kayla is alive,” the family said. “We have sent you a private message and ask that you respond to us privately. We know that you have read our previous communications.”

The Mueller family also revealed Tuesday that their daughter had written a letter in the spring of 2014 in which she talked about the conditions of her captivity. She said she had come to terms with her situation but had not given up hope.

“None of us could have known it would be this long but know I am also fighting from my side in the ways I am able + I have a lot of fight left inside of me,” she wrote. “I am not breaking down + I will not give in no matter how long it takes.”

Appearing before reporters in Prescott, Day, the campus minister at Northern Arizona University, said of Mueller, “She did ordinary things to extraordinary measures.”

Erin Street, who described Mueller as her closest friend and a kindred spirit, said, “We’re all living in a better world because of her.”

An aunt, Lori Lyon, said Mueller was strong, driven and passionate. “She was a free spirit, always standing up for those who were suffering and wanting to be their voice,” Lyon said. “She knew her calling. . . . Kayla has touched the heart of the world.”

Lyon recalled a letter her parents received from their daughter in captivity. “I have come to see there is good in every situation,” she quoted Mueller as saying. “Sometimes you just have to look for it.” Lyon added, “And right now that’s what we’re all trying to do.”

William Branigin and Karen DeYoung in Washington and William Booth in Jerusalem contributed to this report.