Slain Islamic State group hostage Kayla Mueller is honored by her brother Eric Mueller at a vigil in Prescott, Arizona, Feb. 19, 2015. Reuters

Carl Mueller, the father of Kayla Mueller, an American aid worker who was captured by the Islamic State group in Syria in August 2013 and killed this month, told NBC News that the U.S. administration has “put policy in front of American citizens’ lives” by adhering to its rule about not paying ransom money.

President Barack Obama publicly declared the U.S. was doing all it could to save Mueller before she was confirmed dead in early February, when the extremist group formerly known as either ISIL or ISIS claimed she was killed during an airstrike by U.S.-led coalition forces.

Although some Western countries will pay ransom, sometimes a lot of ransom, in exchange for the release of their citizens, the American government will not negotiate with terrorist groups that kidnap people. A U.S. intelligence official told NBC News last August that ransom payments in the “tens of millions of dollars” had been paid to the Islamic State group by certain European governments and relatives of some kidnap victims, saying it constituted a major source of income for the terrorist group.

“We understand the policy about not paying ransom,” Mueller told Savannah Gurthrie in an exclusive interview with the “Today” show. “[O]n the other hand, any parents out there would understand that you would want anything and everything done to bring your child home. And we tried. And we asked. But they put policy in front of American citizens’ lives.”