Russia said Monday that a decision by the EU to ease an oil embargo against Syria in favour of the rebels fighting President Bashar al-Assad was "counter-productive".
"This deepens the impasse and does not contribute to a political solution to problems which have built up over a long time," said Russia's vice-foreign minister Mikhail Bogdanov in comments to the Ria Novosti news agency.
"That is why we think this decision is counter-productive. We consider such unilateral actions to be against the principles of international law."
Bogdanov added that Foreign Minister Sergei Lavrov and US Secretary of State John Kerry would discuss the EU decision during a meeting in Brussels on Tuesday.
EU foreign ministers meeting in Luxembourg formally adopted measures enabling EU companies on a case-by-case basis to import Syrian crude and export oil production technology and investment cash to areas in the hands of the opposition.
Moscow is one of Assad's few remaining backers. It frequently provides the regime with military and other assistance, though it says it opposes foreign intervention in the Syrian conflict.
Along with China, Russia has blocked several UN Security Council draft resolutions threatening sanctions against Assad's regime.