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

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

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

Holder's letter came the day before President Barack Obama is due to deliver a major speech designed to fulfill a promise in his State of the Union speech 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.

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 targets 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.

Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., last month threatened to subpoena the administration for Justice Department legal opinions justifying the killing of U.S. citizens overseas without due process or other constitutional protections. 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 telephoned 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 speech today at the National Defense University.

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

According to Holder's letter, al-Awlaki was the only U.S. citizen the administration "has specifically targeted and killed." Khan was not targeted but was at al-Awlaki's side and killed in the same strike.

Two weeks after al-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 Kenan 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 Afghanistan border, but was later released.

Mohammad's mother, Elena Mohammad, said in a telephone interview she was aware that her son had been killed in a drone strike but said 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."