U.S. Secretary of State Colin Powell has resigned, as the post-election shakeup of President Bush's cabinet continues.

The White House announced a total of four resignations from the cabinet today (Monday).

Along with Mr. Powell, Energy Secretary Spencer Abraham, Education Secretary Rod Paige and Agriculture Secretary Ann Veneman are stepping down.

Mr. Powell told the president in a letter that he believes the time has come for him to "return to private life."

He said he was pleased to be part of a team that, in his words, launched the global war against terrorism, liberated the Afghan and Iraqi people, and brought the world's attention to the problem of nuclear proliferation.

A White House spokesman praised Mr. Powell for doing an outstanding job and said he will stay on until a successor is named.

Mr. Powell, who is 67, was widely expected to resign before the start of President Bush's second term in January. He reportedly differed on some major aspects of the Iraq war with Defense Secretary Donald Rumsfeld.

Cabinet re-shuffles are not unusual for second-term U.S. presidents.

There has been no official word on who will be the next U.S. Secretary of State, but the media, quoting senior administration sources, are speculating that National Security Adviser Condoleezza Rice is a likely candidate.

Ms. Rice is known to be one of President Bush's most trusted aides and a strong supporter of the Iraq war. The 50-year-old Ms. Rice was previously the provost of Stanford University. She is the first woman to hold the National Security Adviser job.

Another name frequently mentioned as a possible successor to Colin Powell is the United States ambassador to the United Nations, John Danforth. The 68-year-old is a former Republican senator.