WASHINGTON -- The Pentagon is trying to assess whether a low-level flight by a Russian bomber over U.S. warships in the Pacific Ocean last weekend was a sign that Moscow is returning to a worrisome "Cold War mind-set," a top defense official told Congress.

General James Cartwright, vice chairman of the U.S. Joint Chiefs of Staff, said officials want to know why a Tu-95 "Bear" bomber flew over the aircraft carrier USS Nimitz and other U.S. vessels in international waters near Japan.

The flight came at a time when the Russian Air Force has begun reinstating the kind of long-range bomber patrols it conducted routinely during the Cold War.

"We're just trying to go back now and look at what message was intended by this overflight," Cartwright told the U.S. Senate Budget Committee on Tuesday. "What are the implications of that activity and how do we best address that?"

The Russian bomber and three others that accompanied it were intercepted by U.S. F-18 fighter jets and escorted as they flew over the U.S. aircraft carrier group, in keeping with normal procedures. Cartwright said the bombers did nothing "unprofessional" and noted that they were in "free and international airspace" at all times.

Admiral Gary Roughead, the chief of U.S. naval operations, told reporters Tuesday that the bombers had given no warning of their intent to fly over the U.S. warships and said that in his view it was "not prudent" to fly over an aircraft carrier.

But he said he did not regard the patrol as provocative. "I know I'm not playing this up very much, but that's the way I see it," he said.

In Moscow, an Air Force spokesman said he not understand the reason for U.S. expressions of concern. "We are surprised by all the clamor this has raised," said the spokesman, Colonel Alexander Drobyshevsky, RIA-Novosti reported.

As the Russians have resumed air patrols in recent months, their aircraft have been intercepted and escorted at various points by British, Norwegian, Danish, Finnish, Canadian and Japanese fighters. Last Saturday, Japanese officials issued a protest to Moscow over what they said was a Russian bomber's violation of Japanese airspace over an island south of Tokyo.

At the U.S. State Department, spokesman Sean McCormack said Tuesday that the Russian bomber flights were not seen as a threat.

"I don't think we view it as a particular threat. It is something that we watch closely, and I'm sure folks over at the Pentagon watch it as well," he said.

Any U.S. expressions of concern to Russia would probably be carried out through military channels, McCormack said.

Senator Bill Nelson, a Democrat who raised the bomber flyover during the Senate hearing, said the maneuver "sounds pretty provocative to me." He said the Armed Services Committee, of which he is a member, would look into the issue.

In light of Russia's renewed military buildup, some U.S. military officials in Europe have cautioned the Pentagon against its planned withdrawal of two divisions from Europe. But other defense officials, including Defense Secretary Robert Gates, a longtime expert on Soviet issues, have played down the threat, interpreting it only as a sign of Russia's desire to reassert its importance on the world stage.

At the Senate Budget Committee hearing, Republican Senator Pete Domenici said he was worried about the threat and concerned that U.S. spending to contain militant Islam would siphon funds needed to deal with a possible return of problems with Russia. "Confrontations between us and Russia that didn't exist before are real today," Domenici said.

Asked about U.S. preparations for a potential Russian threat, Cartwright called it "one of the things that would keep me up at night."

The Senate discussion was the latest sign of U.S. concern about friction with Moscow over issues such as U.S. plans for an anti-missile system in Eastern Europe, looming Kosovo independence and Washington's strengthened relations with Ukraine and Georgia.

Russia also is unhappy with continued U.S. support for expansion of the NATO military alliance. President Vladimir Putin said Tuesday that Russia could train its nuclear missiles on Ukraine if the country joined NATO.

Asked his reaction to Putin's statement, McCormack said, "There he goes again."

In reply to a question in Congress on Wednesday, U.S. Secretary of State Condoleezza Rice said Putin's rhetoric was reprehensible and unacceptable.

LAT, Reuters