Susan Rice, leading contender for the post of US secretary of state to succeed Hillary Clinton, on Thursday took her name out of the reckoning in a letter to the president.

Rice said she asked the president that "you no longer consider my candidacy at this time" as the "confirmation process would be lengthy, disruptive and costly". The president accepted Rice's decision, saying he "deeply regrets the unfair and misleading attacks on Susan Rice", said a White House statement.

Rice will continue as US ambassador to the UN. And, as per fresh speculation, she might at a later date be named national security adviser, which won't require senate confirmation.

Senator John Kerry, senate foreign relations committee head who played Mitt Romney to prepare Obama for the presidential debates, has emerged as the frontrunner for the job.

Rice's decision comes after Republicans threatened to use every means possible to block her appointment. They believe Rice misled the country on the death of four US officials in an attack on the country's mission in Benghazi, Libya, on September 11.

Actually, she had only read from a memo prepared for her by the intelligence community.