United States' Ambassador to the United Nations John Bolton has resigned.
The resignation was being described as a fallout of the Republican Party's defeat in the November 7 elections.
US President George W Bush accepted Bolton's resignation immediately after he submitted it on Monday 'with deep regret'.
The appointment was subject to the confirmation of by the US Senate, now under the control of the Democratic Party, which has accused the ambassador of being a bully and of pressuring subordinates to align their views with him.
Bolton's temporary appointment last year had allowed him to bypass the Senate confirmation process.
Commending the role played by Bolton, the White House, in a statement, said, the President credited Bolton with leading negotiations in the UN Security Council that resulted in unanimous resolutions on North Korean military and nuclear activities, a resolution calling on Iran to suspend the enrichment and reprocessing of uranium, and a UN peacekeeping commitment to Sudan.
He was appointed to the post in August 2005 during a period when the Senate, which normally would vote on the nomination, was in recess. Under the US Constitution, a president may make temporary recess appointments without Senate confirmation.
The President re-nominated him on November 9, but administration officials believed that his nomination did not have enough support in the Senate Foreign Relations Committee to come to the full Senate for a confirmation vote.
President Bush said some senators were practicing stubborn obstructionism by 'obstructing his confirmation' despite Bolton having the support of the majority of the Senate.
''Their tactics will disrupt our diplomatic work at a sensitive and important time,'' President Bush said.
White House Press Secretary Tony Snow blamed Bolton's difficulties in the Senate were on partisanship and not performance.
The exact date of Bolton's departure has not been announced and under the US law, he can continue to serve until the 110th Congress convenes in January 2007.
Until Bolton's successor is confirmed, Alejandro Wolff, the deputy US representative to the United Nations, is expected to serve as acting US ambassador to the United Nations.UN Secretary-General Kofi Annan commended Bolton for 'doing the job he was expected to do'.