The US Senate on Saturday confirmed President Barack Obama's nominee to be ambassador to Moscow, Michael McFaul, after a delay tied to US missile defense plans.

Lawmakers approved McFaul, who had served as the chief Russia hand on Obama's National Security Council, in a unanimous voice vote.

The confirmation came after Republican Senator Mark Kirk lifted his "hold" on the nomination over concerns that Russo-US cooperation on the missile shield could see Moscow obtain classified information that it might turn around and share with Iran.

Kirk lifted his objections after the White House wrote him a letter assuring him that it will "not provide Russia with sensitive information about our missile defense systems that would in any way compromise our national security."

Specifically the White House told Kirk that "under no circumstances" would the United States provide hit-to-kill technology and interceptor telemetry to Russia.

McFaul was considered one of the architects of the so-called "reset" of Soviet-US relations that took place shortly after the president took office in early 2009.

Among key events in the warming of the two countries' relationship in recent years has been the signing and ratification of the new START treaty on nuclear disarmament, cooperation on sanctions against Iran and a strengthening of commercial relations.

Kirk's hold had threatened a vacant seat in the critical Moscow post, with the current US ambassador to Russia, John Beyrle, due to leave the job this month.