The director of the US National Security Agency (NSA) will leave the post in March, White House spokesman Jay Carney confirmed on Thursday.

General Keith Alexander, who in addition to heading the NSA also heads US Cyber Command, on Thursday made public his decision to leave the NSA. Mr. Alexander has been director of the agency since 2005 and is its longest-serving head. He’s been head of the US Cyber Command since 2010.

“General Alexander has served an extraordinary tenure and capably led these agencies through critical periods of growth and transition,” Mr. Carney said. Mr. Alexander spoke to President Barack Obama a few weeks ago about his plans to retire, he added.

The spokesman also denied that Mr. Alexander’s resignation had anything to do with the pace of reform at the agency or Mr. Obama’s demand for transparency at the NSA.

Mr. Carney also responded to a newspaper report saying NSA created a secret unit with the CIA to pinpoint and kill particularly hard-to-find terrorism targets.

The agency “is a foreign intelligence agency” focused on discovering and developing intelligence about valid foreign intelligence targets, including terrorists.

“Its activities are directed against these valid foreign intelligence targets in response to requirements from US leaders in order to protect the nation and its interests from threats such as terrorism and the proliferation of weapons of mass destruction,” he said.

The Washington Post reported on the secret unit on Thursday, saying documents leaked by former NSA contractor Edward Snowden were the source of the information. The Post revealed the extent to which the NSA is involved in the government’s drone strike programme.

The joint NSA-CIA unit, known as the Counter-Terrorism Mission Aligned Cell, has been involved in the killing of more than 3,000 people in Pakistan, including thousands of alleged militants, reported the Post.

As one example, the paper detailed the collaboration between the CIA (Central Intelligence Agency) and the NSA to kill al-Qaeda leader Hassan Ghul in May 2011.

The NSA set up a surveillance operation in north-west Pakistan, the Post reported, secretly seizing audio files and control of laptops in order to determine Ghul’s location in the country.

The government has not confirmed its role in Ghul’s death.

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