The Obama administration acknowledged Wednesday that it has killed four Americans in overseas counterterrorism operations since 2009, the first time it has publicly taken responsibility for the deaths.

Although the acknowledgment, contained in a letter from Attorney General Eric H. Holder Jr. to Congress, does not say how the four were killed, three are known to have died in CIA drone strikes in Yemen in 2011: Anwar al-Awlaki, his 16-year-old son and Samir Khan.

The fourth — Jude Kennan Mohammad, a Florida native indicted in North Carolina in 2009 — was killed in Pakistan, where the CIA has operated a drone campaign against terrorism suspects for nearly a decade. His death was previously unreported.

Holder’s letter came the day before President Obama is due to deliver a major speech designed to fulfill a promise in his State of the Union address in January to make elements of his controversial counterterrorism policies more transparent and accountable to Congress and the American public.

Obama is also under pressure to explain how he intends to make even modest progress on other priorities that were centerpieces of a pledge he made at the beginning of his first term. At the top of that list is closing the Guantanamo Bay prison, where 103 of the 166 detainees still in custody are on a hunger strike.

The administration is planning to restart the transfer of the detainees, 86 of whom have been cleared to leave. A White House official said without elaboration that Obama “will announce a number of specific steps to advance” his goal of closing the facility.

In addition to disclosure of the four killings, Holder wrote that Obama has approved classified briefings for Congress on an overall policy document, informally called the “playbook.” The document, more than a year in the making, codifies the administration’s standards and processes for its unprecedented program of targeted killing and capture of terrorism suspects outside of war zones.

Nearly 400 drone strikes, in Pakistan, Yemen and Somalia, have been launched by the CIA and U.S. military forces during Obama’s presidency. Although the administration has acknowledged the existence of the drone program and outlined its justification under international and domestic law, specific operations are considered classified.

The secrecy surrounding the program — including the criteria for choosing targets — has led to widespread opposition from international law and human rights advocates and, increasingly, from Congress and the public. Although the administration has stressed the precision accuracy of drones, independent groups have charged that thousands of civilians have been unintentionally killed.

Congressional and public criticism reached a crescendo this year when Obama nominated John Brennan, then his principal counter­terrorism adviser, as CIA director. Before they would confirm Brennan, lawmakers demanded access to Justice Department legal opinions justifying the killing of U.S. citizens overseas without due process or other constitutional protections. Although the documents were made available to the Senate and House intelligence committees, other members insisted that they had a right to the information.

One of them was Senate Judiciary Committee Chairman Patrick J. Leahy (D-Vt.), who threatened last month to subpoena the administration for the opinions. After that threat, Leahy said in an interview, the documents were produced for the committee in a classified meeting.

Leahy said Wednesday afternoon that Holder called him to say he would receive a letter with information about the four killings and to tell him about upcoming briefings on the classified playbook. Although Holder’s letter was addressed to Leahy, it was copied to the rest of the Judiciary Committee.

“I think it’s a significant effort at openness,” Leahy said. He said he also received a call from the White House inviting him to Obama’s Thursday speech at the National Defense University at Fort McNair.

Others were less certain that critics would be satisfied.

“The desire to put this on a normal, rule-of-law footing keeps clashing with the imperatives of national security, which entail extreme institutional secrecy,” said Jack Goldsmith, former director of the Justice Department’s Office of Legal Counsel. “That clash has been going on since the first day of the administration.”

Prior to the Obama administration, the only known American killed by a drone strike was Kamal Derwish, who died in a strike launched in Yemen in 2002 under President George W. Bush.

In September 2011, Obama announced the death of Awlaki, a New Mexico-born cleric described as the foreign operations director for Yemen-based al-Qaeda in the Arabian Peninsula, known as AQAP. Although Obama did not claim U.S. responsibility, the fact that Awlaki was killed by a CIA drone was one of the worst-kept secrets in Washington.

According to Holder’s letter, Awlaki was the only U.S. citizen the administration “has specifically targeted and killed.” Khan, who edited an AQAP online magazine that provided bomb-building instructions allegedly used to carry out the Boston Marathon attack, was not targeted but was at Awlaki’s side and killed in the same strike.

Two weeks after Awlaki’s death, his 16-year-old son, Abdulrahman — who had gone to the Yemeni desert in search of his father — was killed in a drone strike meant for someone else. That strike was similarly un­acknowledged, although a senior administration official privately characterized it as a “mistake.”

The fourth American death, Jude Kennan Mohammad, was previously unreported. According to an information sheet released by the Justice Department, the former North Carolina resident was charged in 2009 with conspiracy “to provide material support to terrorists, including currency, training, transportation and personnel” and “to murder, kidnap, maim and injure persons abroad.”

Mohammad had fled the United States for Pakistan in the fall of 2008. According to Pakistan news accounts, the 20-year-old Mohammad, whose father was Pakistani, was detained by authorities when he tried to enter a tribal region near the Afghan border but was later released.

Mohammad’s mother, Elena Mohammad, said in a telephone interview that she was aware that her son had been killed in a drone strike but that she got the news from people in Pakistan, not U.S. authorities. She said she had no details on when and where her son was killed.

“I dealt with that, and I don’t have to deal with it anymore because it’s already over with,” she said. “So whatever transpired I don’t want it back in my life anymore. It’s gone. There are no questions. I don’t have to hear any authorities; the FBI has finished coming to my house. It’s over. That’s it.”

In regard to Guantanamo, the large Yemeni population there — at least 84 of the 166 detainees — could be one area where Obama chooses to act. After the failed attempt to bomb a commercial plane over Detroit on Dec. 25, 2009, a plot that was linked to Awlaki and AQAP, the president suspended all transfers of detainees to Yemen.

The government of Yemen and human rights groups have urged Obama to lift the moratorium and begin the staggered repatriation of some of these detainees. Of the Yemenis held at the military detention center in Cuba, 26 have been cleared for transfer and 30 others could be sent home if security conditions in the country improved, according to U.S. officials

Yemen President Abed Rabbo Mansour Hadi recently set up a detainee affairs committee made up of cabinet ministers and officials in the defense, intelligence and internal security agencies to manage any return and work with the United States to create and implement a resettlement plan, according to Mohammed Albasha, a spokesman for Yemen’s Embassy in Washington.

An additional 30 detainees of various nationalities were also cleared for transfer by an inter­agency task force in the first year of Obama’s first term but remain at the facility.

Greg Miller and Julie Tate contributed to this report.