A Pentagon official working on closing the notorious Guantanamo Bay detention center has resigned.

Phillip Carter was appointed deputy assistant secretary of defense for detainee policy in April, but resigned last week due to "personal and family" reasons, said Pentagon spokesman Bryan Whitman on Wednesday, AFP reported.

Carter's departure comes days after President Barack Obama acknowledged that his administration would not be able to close the "war on terror" camp at the US naval base in Cuba by the January 22, 2010 deadline that he had set.

Obama had vowed during his first week in office in January that he would close Guantanamo within a year of taking office, saying that the prison camp did not adhere to US standards on human and civil rights and underlined his desire to break with the policies of his predecessor, George W. Bush.

Some 215 suspects remain detained in Guantanamo.

The White House announced on November 13 that Obama's top lawyer Greg Craig — a veteran Washington hand who led the effort to close Guantanamo — would resign on January 3.

His resignation came just after US Attorney General Eric Holder's announcement that the alleged mastermind of the September 11, 2001 attacks, Khalid Sheikh Mohammed, and four others held at Guantanamo Bay, will be tried in a civilian court in New York.

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