The U.S. presidential candidates assailed Russia on Tuesday, with Democrat Barack Obama saying Moscow had engaged in "evil" behavior and Republican John McCain saying it was "maybe" an evil empire.

The two, taking part in a presidential debate, were asked the barbed question "Do you think that Russia under Vladimir Putin is an evil empire?" and were asked to reply "yes" or "no."

Both stopped short of "yes" or "no" but made plain they have problems with Russia.

"I think they''ve engaged in an evil behavior and I think that it is important that we understand they''re not the old Soviet Union but they still have nationalist impulses that I think are very dangerous," Obama said.

"Maybe," McCain said, adding: "If I say yes, then that means that we''re reigniting the old Cold War. If I say no, it ignores their behavior."

Putin was president of Russia until May this year, when he handed over to Dmitry Medvedev and took the post of prime minister.

In reply to an earlier question in the debate, McCain and Obama denounced Russia''s military push in August into Georgia, the first such offensive outside its territory since the 1991 collapse of the Soviet Union. Moscow''s action followed a crackdown by Georgia on rebels of the breakaway region of South Ossetia.

"I think we can deal with them (the Russians) but they''ve got to understand that they''re facing a very firm and determined United States of America that will defend our interests and that of other countries in the world," McCain said.

McCain and Obama were taking part in the second of three presidential debates ahead of the November 4 election.

Reagan used the phrase "evil empire" for the first time in a March 8, 1983, speech to the National Association of Evangelicals in Orlando, Florida.

Referring to the "aggressive impulses of an evil empire," he said it would be wrong to simply call the arms race a giant misunderstanding "and thereby remove yourself from the struggle between right and wrong and good and evil."