Russian bombers had not "buzzed" a US aircraft carrier since 2004

The unnamed officials told news agencies that the Russian bombers had flown over the USS Nimitz in the western Pacific on Saturday.

Four F-18 jets escorted the bombers out of the area, they added.

Russia resumed long-range bomber flights last August, in a move regarded as a flexing of military muscle.

Russian officials were not immediately available to comment on Saturday's incident.

It was the first time a Russian bomber had flown over a US aircraft carrier since July 2004.

Meanwhile, Japan has lodged a complaint with Moscow over allegations that a Russian bomber, thought to be one of those involved in the Nimitz fly-over, intruded into Japanese airspace on Saturday.

The incident comes amid renewed tensions between Moscow and Washington over American plans for a missile defence system based in Poland and the Czech Republic.