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Jordan's Queen Rania holds a picture of recently executed Jordanian pilot Muath al-Kasasbeh, with the words in Arabic reading "Muath is a martyr of right", during a march after Friday prayers in Amman February 6, 2015. Thousands of Jordanians gathered to show their loyalty to the King and to show solidarity with the family of the pilot, Muath al-Kasasbeh, killed by Islamic State. REUTERS/Petra News Agency

U.S. hostage Kayla Mueller has reportedly been killed on Friday. Her family received the news over the weekend in an email from Islamic State, which had held Mueller hostage for 18 months.

Mueller’s family said on Tuesday that it had received the email and a photograph that apparently confirmed her death. The family issued a statement to say that they were “heartbroken” to share the received confirmation that Mueller had “lost her life." The family calls Mueller as a “compassionate and devoted humanitarian.” The statement also says that she dedicated the whole of her young life to helping those in need of freedom, justice and peace.

National Security Council spokeswoman Bernadette Meehan confirmed that IS had sent the private message to the family over the weekend. According to CNN, she said that it was “concluded” that Mueller had been killed once the received information had been authenticated by the U.S. intelligence community. The 26-year-old was apparently killed when Jordanian fighter planes bombed a building where she was being held outside Raqqa.

Mueller was believed to be the last U.S. hostage held by IS. However, White House spokesman Josh Earnest said on Tuesday that other American hostages were being held in the parts of Syria and Iraq controlled by the militant organisation. Mueller was captured in August 2013 when she was leaving a northern Syrian hospital. She used to work in Turkey for providing humanitarian assistance to refugees from Syria's civil war.

According to the White House, U.S. President Barack Obama talked to Mueller's parents and offered condolences. Obama said in a White House statement that the United States would find and bring to justice the terrorists responsible for Mueller's captivity and death no matter how long it took. "ISIL is a hateful and abhorrent terrorist group whose actions stand in stark contrast to the spirit of people like Kayla," Reuters quotes Obama who used an acronym for the extremist group.

Reuters reports that British photojournalist John Cantlie is among the hostages believed to have held by IS. He was captured in northern Syria in November 2012. U.S. journalist Austin Tice disappeared in Damascus in August 2012. However, it is not confirmed if he is still alive. Neither is it confirmed if he is being held hostage. His family renewed its campaign last week to draw attention to his case.

Contact the writer: s.mukhopadhyay@IBTimes.com.au