One week after a U.S. military airstrike killed a 16-year-old American citizen in Yemen, no one in the Obama administration, Pentagon or Congress has taken responsibility for his death, or even publicly acknowledged that it happened.

The absence of official accountability for the demise of Abdulrahman al-Awlaki, a Denver native and the son of an al-Qaeda member, deepens the legal and ethical murkiness of the Obama administration’s campaign to kill alleged enemies of the state outside of traditional war zones.

Unlike the secretive U.S. airstrikes that have killed hundreds of foreigners in Pakistan, Somalia and Yemen, this case involved an American teenager. He was killed by the U.S. military in a country with which Washington is not at war.

Officials throughout the U.S. government, however, have refused to answer questions for the record about how or why Awlaki was killed Oct. 14 in a remote part of Yemen, along with eight other people.

The Obama administration has asserted the right to launch attacks against al-Qaeda members anywhere in the world, saying there is no difference between a battlefield in Afghanistan and a suspected terrorist hideout in Yemen or Somalia.

But when U.S. forces kill civilians or operations go awry in traditional war zones such as Afghanistan or Iraq, the military routinely conducts official investigations. The results are often declassified and released as public records.

“If the government is going to be firing Predator missiles at American citizens, surely the American public has a right to know who’s being targeted, and why,” said Jameel Jaffer, deputy legal director of the American Civil Liberties Union.

The official silence about the death of the American teenager contrasts with the Obama administration’s eagerness to trumpet another airstrike in Yemen two weeks earlier. In that case, armed drones controlled by the CIA killed the teen’s father, Anwar al-Awlaki, a dual Yemeni-American citizen who worked as a propagandist for al-Qaeda in the Arabian Peninsula.

U.S. and Yemeni counter­terrorism officials had been searching for the elder Awlaki for years, describing him as a dangerous terrorist who posed a direct threat to the United States.

“The death of Awlaki is a major blow to al-Qaeda’s most active operational affiliate,” Obama said hours after the Sept. 30 airstrike.

“This country is much safer as a result of the loss of Awlaki,” said Defense Secretary Leon E. Panetta.

“I’m glad they did it,” said Sen. John McCain (R-Ariz.), vice chairman of the Armed Services Committee.

In the case of Awlaki’s son, however, U.S. officials have been willing to talk only on the condition of anonymity because they were not authorized to speak publicly about the matter.

Two U.S. officials said the intended target of the Oct. 14 airstrike was Ibrahim al-Banna, an Egyptian who was a senior operative in Yemen’s al-Qaeda affiliate.

Obama administration lawyers have said the military and CIA can target suspected terrorists outside of war zones only if they represent a direct threat to U.S. interests. But the criteria they use remain shrouded in mystery. There is no external review by the courts.

One administration official described the younger Awlaki as a bystander, in the wrong place at the wrong time. “The U.S. government did not know that Mr. Awlaki’s son was there” before the order to launch the missile was given, the official said.

Another U.S. official said the airstrike was launched by the military’s secretive Joint Special Operations Command, or JSOC. It remains unclear whether the missile was fired by a remotely piloted drone or a fighter jet.

Two U.S. officials, again speaking on the condition of anonymity, suggested in the days after the strike that Abdulrahman al-Awlaki was in his 20s, calling him a “military-age male.” Such a description, under the laws of war, might make it easier to justify his killing.

On Tuesday, however, Awlaki’s family released a copy of his U.S. birth certificate showing that he turned 16 on Aug. 26.

Defense Department officials declined to answer questions about the airstrike or say whether any official investigations or reviews were underway.

“We do not discuss the specifics of our operations,” said Navy Capt. John Kirby, a Pentagon spokesman.

Kenneth S. McGraw, a spokesman for the Special Operations Command in Tampa, referred queries to the U.S. Central Command, the joint headquarters responsible for operations in Yemen.

Maj. T.G. Taylor, a Central Command spokesman, also declined to talk about the Oct. 14 airstrike. “Anytime we conduct operations, it’s of utmost importance to us to avoid civilian casualties or collateral damage,” Taylor said.

The State Department said Tuesday that it could not confirm the younger Awlaki’s death. Tommy Vietor, a spokesman for the National Security Council, declined to comment, although he spoke in general terms about the dangers of U.S. citizens traveling in Yemen.

The younger Awlaki was the third U.S. citizen killed by the U.S. government in Yemen in recent weeks. The Obama administration has said that U.S. citizens do not have immunity from being targeted for death if they are al-Qaeda members. In addition to the elder Awlaki, the Sept. 30 CIA drone attack killed Samir Khan, an al-Qaeda propagandist from Charlotte.

All individuals targeted by the JSOC must be approved in advance by the National Security Council, said a senior U.S. official. Afterward, the JSOC files detailed reports through the Special Operations Command and then to the Joint Staff in the Pentagon.

By comparison, the CIA’s covert armed drone program has come to be treated as an open secret in Washington — not formally acknowledged, but defended and described in abundant detail by U.S. officials in unofficial conversations.

Congressional officials said that if the Oct. 14 strike had been executed by the CIA, the Senate and House intelligence committees would likely have been notified right away. On Thursday, military officials presented a closed briefing on the JSOC airstrike to members of the Senate Armed Services committee. Members of the panel declined to discuss details.

Members of the House Armed Services Committee would not say whether the panel had been briefed or was reviewing the 16-year-old’s death.

Staff writers Greg Jaffe and Greg Miller contributed to this report.