Moscow and Washington have traded fierce diplomatic blows over Syria with US charges that Russia was pushing its ally into civil war and the Kremlin accusing the White House of being emotional.

The brisk exchange came as President Vladimir Putin prepared to face a grilling on Friday from the leaders of Germany and France during his first tour abroad since his May 7 inauguration to a controversial third term.

Russia has made it clear from the start that Putin will not be swayed by Western and Arab world anger over his refusal to back action against a Middle East regime that Moscow has held patronage over since Soviet times.

"Russia's position is well-known. It is balanced and consistent and completely logical," Interfax quoted Putin's spokesman Dmitry Peskov as saying.

"So it is hardly appropriate to talk about this position changing under someone's pressure."

But US Secretary of State Hillary Clinton used some of her most explicit language to date to indicate that Washington's patience with Moscow was running thin because of its refusal to commit to tougher UN Security Council measures.

The Russians "are telling me they don't want to see a civil war. I have been telling them their policy is going to help contribute to a civil war," she told a mainly student audience on a visit to Copenhagen.

"We have to bring the Russians on board because the dangers we face are terrible. We know it actually could get much worse than it is."

Russia insists that it is not supporting President Bashar al-Assad's government but respect for international law and the policy of non-intervention in internal conflicts.

That argument has found less currency with foreign powers following the slaughter last weekend of 108 civilians - almost half of them children - in the Syrian town of Houla that Moscow partially blamed on both sides. [AFP]