President Barack Obama has nominated a longtime White House foreign policy adviser to the No. 2 post at the State Department.

Tony Blinken joined the White House in 2009 as a top aide to Vice President Joe Biden. He later became Obama's deputy national security adviser and a key player on a range of foreign policy issues, including the fight against the Islamic State militants in Iraq and Syria.

If confirmed by the Senate, Blinken would replace William Burns, who retired earlier this year. It's unclear whether the Senate will vote on his nomination before the end of the year or after the new Republican-led Congress takes over in January.

The White House has not yet named a replacement for Blinken.