The Foreign Ministry warned that Russia would not cooperate with European Union sanctions requiring EU governments to search vessels suspected of carrying weapons into Syria, a defiant stance that is likely to spark anger in the West.
EU governments adopted the new embargo rules last week in an effort to prevent arms from reaching Syria, where 16 months of violence that Western nations blame mostly on the government has killed more than 18,000 people by some estimates.
Russia has blocked efforts to threaten the government with UN Security Council sanctions and has criticized Western embargoes.
The Foreign Ministry said Moscow does "not intend to take any part in the measures to implement the EU decisions aimed against Syria."
"We … will not consider appeals and give consent to searches of vessels sailing under the Russian flag nor to the application of other restrictive measures to them," Foreign Ministry spokesman Alexander Lukashevich said in a statement Saturday.
Russia has faced sharp Western criticism over arms deliveries to the Syrian government. President Vladimir Putin said last month that Moscow was not supplying any weapons that could be used in a civil conflict.
A cargo ship that Russia said was carrying three repaired helicopters and air defense systems to Syria turned back toward Russia last month when its London-based insurance company withdrew coverage.
Russian officials subsequently said the cargo ship's Curacao flag would be replaced by a Russian one, and the vessel was initially reported to have headed toward Syria again.
But Interfax later reported that the helicopters had been off-loaded in Russia.
Also Saturday, Foreign Minister Sergei Lavrov warned that international support for Syrian rebels would lead to "more blood," and he said the government could not be expected to willingly give in to its opponents.
"Pressure must be put on everyone," Lavrov said at a joint news conference with Japanese Foreign Minister Koichiro Gemba after talks in Sochi, Putin's summer base.
"Unfortunately, our Western partners prefer to do something a bit different and essentially, along with some countries neighboring Syria, encourage, support and direct the armed fight against the regime," he said. "The price of all this is still more blood."
Gemba said it is a "very serious moment" in Syria and it is primarily up to the government to stop the bloodshed.
"The position of the Russian side has great influence, and there is also the voice of the international community. We are counting on a constructive Russian position," he said, speaking through an interpreter.
Lavrov said that Russia was calling on the government to "take the first steps" but that the rebels should not take advantage of any such government actions by occupying cities and towns.
Lavrov also said Russia has made no agreement to grant Syrian President Bashar Assad asylum and is "not even thinking about" doing so.