US President Barack Obama has formally announced his close confidante Susan Rice as his next national security adviser.

Obama made the announcement, which is seen as a major change in his foreign policy, on Wednesday.

He lauded Rice as an "exemplary public servant," implicitly shrugging off Republican criticism of her qualifications.

Rice, currently ambassador to the UN, would take over from Tom Donilon in July, in an appointment which defies Republican claims that she misled Americans over the attack on the US mission in Benghazi.

He also nominated Samantha Power, a Pulitzer Prize-winning author, former White House aide and Harvard professor, as UN ambassador.

Rice's appointment as Obama's top security adviser does not require Senate confirmation.

Obama had wanted to name Rice as his secretary of state, but she ran into heavy opposition from Republicans over remarks she made in the aftermath of the September 11, 2012 attack on the US mission in Benghazi, Libya, that killed four Americans, including Ambassador Christopher Stevens.

Rice withdrew her name from consideration for the top diplomatic post in December.

Donilon, who served for more than four years as Obama's top national security adviser, will leave in early July, a White House official said.

The shake-up comes as the Obama administration struggles with its response to the civil war in Syria.

Source: Reuters