U.S. fighter planes intercepted two Russian bombers flying unusually close to an American aircraft carrier in the western Pacific during the weekend, The Associated Press has learned.

A U.S. military official says that one Russian Tupolev 95 buzzed the aircraft carrier USS Nimitz twice, at a low altitude of about 2,000 feet, while another bomber circled about 50 nautical miles out. The official was speaking on condition of anonymity because the reports on the flights were classified as secret.

The Saturday incident, which never escalated beyond the flyover, comes amid heightened tensions between the United States and Russia over U.S. plans for a missile defense system based in Poland and the Czech Republic.

Such Russian bomber flights were common during the Cold War, but have been rare since.

The bombers were among four Russian Tupolev 95s launched from Ukrainka in the middle of the night, including one that Japanese officials say violated their country's airspace over an uninhabited island south of Tokyo.

U.S. officials tracked and monitored the bombers as two flew south along the Japanese coast, and two others flew farther east, coming closer to the Nimitz and the guided missile cruiser USS Princeton.

As the bombers got about 500 miles out from the U.S. ships, four F/A-18 fighters were launched from the Nimitz, the official said. The fighters intercepted the Russian bombers about 50 miles south of the Nimitz.

At least two U.S. fighters trailed the bomber as it came in low over the Nimitz twice, while one or two of the other U.S. fighters followed the second bomber as it circled.

The official said there were no verbal communications between the U.S. and the Russians, and the Pentagon has not heard of any protests being filed by the United States. Historically, diplomatic protests were not filed in such incidents because they were so common during the Cold War era.

This is the first time Russian Tupolevs have flown over or interacted with a U.S. carrier since 2004.