WASHINGTON - The Obama administration confirmed for the first time Wednesday that four Americans have died in U.S. drone strikes since 2009, but it sought to justify the killing of only one - a senior leader of al-Qaeda's Yemen-based affiliate - and said nothing about the others except to acknowledge indirectly that they had been killed by accident.

The confirmation came in a letter to Senate Judiciary Committee Chairman Patrick J. Leahy (D., Vt.) from Attorney General Eric H. Holder Jr. that was released one day before President Obama is to deliver a major counterterrorism speech in which he is expected to disclose more details of the secret targeted-killing program.

In the same speech, Obama is also likely to outline measures he plans to take to fulfill a recently renewed pledge - first made after his 2009 inauguration - to close the military-run detention center at Guantanamo Bay, Cuba.

The identities of three of the four Americans disclosed in Holder's letter were known previously - Anwar al-Awlaki, a cleric who has been tied to a range of terrorist plots; Samir Khan, a former resident of Charlotte, N.C., who was editor of al-Qaeda's online magazine; and Abdul Rahman Anwar Awlaki, the teenage son of Awlaki. The elder Awlaki and Khan were killed in the same attack; the younger Awlaki died in a separate strike two weeks later.

The inclusion of the fourth American, Jude Kenan Mohammad, marked the first time that the United States has acknowledged his death, which reportedly occurred in a November 2011 drone strike in Pakistan's tribal agency of South Waziristan.

Mohammad, a former resident of Raleigh, N.C., was one of eight men who remained on the loose after they were indicted by a federal grand jury in North Carolina in July 2009 on charges of plotting to attack the Marine Corps base at Quantico, Va. According to the indictment, Mohammad "departed the United States to travel to Pakistan to engage in violent jihad" in October 2008.

'It was just'

The decision to kill the elder Awlaki "was lawful, it was considered, and it was just," Holder wrote, reciting a list of attacks that Awlaki allegedly oversaw. They included a failed 2009 Christmas Eve attempt by a Nigerian man to blow up a passenger jet over Detroit with a bomb hidden in his underwear.

The three others, however, "were not specifically targeted by the United States," Holder said, indirectly verifying that they were killed by accident. He made no further references to the three.

Holder said his letter was only one of a number of steps the administration would be taking to fulfill pledges that Obama has made to provide "Congress and the American people with as much information as possible about our sensitive counterterrorism operations."

'Exacting'

He also disclosed that Obama recently approved "exacting standards and processes for reviewing and approving operations to capture or use lethal force against terrorist targets outside the United States and areas of active hostilities; these standards and processes are either already in place or are to be transitioned into place."

While the procedures will be briefed to select lawmakers, they will remain secret, Holder said, adding that they "make clear that a cornerstone of the administration's policy" is that "lethal force should not be used when it is feasible to capture a terrorist suspect."

Nearly 4,000 people are estimated to have died in drone strikes that began under President George W. Bush and were intensified by Obama. The vast majority have been launched by the CIA in Pakistan's tribal area bordering Afghanistan, where al-Qaeda's central leaders, the Afghan Taliban and its allies, and Pakistani Islamist groups are based.

The CIA and the military's U.S. Special Operations Command have also staged drone strikes in Yemen and Somalia.