US President Barack Obama is expected to nominate Senate Foreign Relations Committee Chairman John Kerry to succeed Hillary Clinton as secretary of state.
Mr Kerry, the Democratic nominee for president in 2004 and a stalwart Obama supporter, had been widely tipped as the likely candidate.
The announcement of Mr Kerry's nomination could come as early as mid-week, although it could be delayed to avoid the impression of an overly-hasty return to politics after the Sandy Hook school killings.
A source also said the White House is leaning toward unveiling Mr Kerry's nomination as part of a high-profile package that would include Mr Obama's pick for defence secretary.
Former Republican US Senator Chuck Hagel is the top candidate to take over the Pentagon and the White House's vetting process for him is virtually complete, the source said.
The President met Mr Hagel at the White House on 3 December to discuss the post and has also spoken to Vice President Joe Biden.
While Mr Obama is said to be generally comfortable with Mr Hagel's foreign policy views, there is some concern within the administration that his record of occasional criticism of Israel could create problems in the confirmation process.
Mrs Clinton, consistently rated as the most popular of Mr Obama's cabinet, intends to step down toward the end of January when he is sworn in for a second term.
The State Department said yesterday she was recovering from a concussion suffered after she became dehydrated with a stomach virus.
There is widespread speculation that Mrs Clinton will seek the Democratic nomination for president in 2016.
Mr Kerry's nomination would close the books on a political firestorm that engulfed US Ambassador to the UN Susan Rice, the candidate seen as the early favourite for the top diplomatic job.
A close Obama confidante, Ms Rice withdrew her name from consideration after heavy fire from Republicans for remarks she made in the aftermath of an 11 September attack on the US mission in Benghazi, Libya, in which four Americans were killed, including Ambassador Chris Stevens.
Republicans have criticised the Obama administration for its early public explanations of the attack, and trained most of their firepower on Ms Rice, who went on television to say that preliminary information suggested the assault was the result of protests over an anti-Muslim video made in California rather than a premeditated strike.
Ms Rice, defended by Mr Obama and other senior members of the administration, said on Thursday she was withdrawing her name from consideration to avoid a potentially lengthy and disruptive confirmation process in the US Senate.