Russia said Friday that decisions made at a Friends of Syria meeting in Rome this week, which saw the United States pledge direct aid to Syrian rebels, encouraged "extremists" who want to seize power by force.
"The decisions made in Rome as well as the statements, both in letter and spirit, give direct encouragement to extremists to take power by force, despite the unavoidable suffering of ordinary Syrians," the foreign ministry said in a statement.
At the meeting with the opposition National Coalition on Thursday, the United States announced that it would for the first time provide direct aid to Syrian rebels in the form of food and medical assistance.
It also announced $60 million in extra assistance to the political opposition.
Russia denies that it has a policy of propping up Syrian President Bashar al-Assad during the two-year conflict but has not backed calls for him to stand down.
"In our opinion, the urgent task today is an immediate cessation of bloodshed and any violence and a shift to political dialogue which is foreseen by the Geneva Communique," the statement said, referring to a transition plan agreed by world powers in June 2012.
"We are convinced that this is exactly what will allow to realise the goals that are most important for Syrians -- to secure a peaceful and democratic development of a single Syria in the interests of all its nationals, without any exception."
Russia's UN Ambassador Vitaly Churkin added that the US decision, announced in Rome by Secretary of State John Kerry, was "unfortunate."
"The US... chooses not to sully its hands with direct supply of weapons to the armed groups, because among them are terrorists and others with whom the US would prefer not to be associated," he told pro-Kremlin television channel RT.
"But at the same time they give a wink and a nod to those who provide direct military aid to rebel armed groups. All this is very unfortunate, because it takes attention away from the need to enter a political dialogue."
Churkin said it was time for the Syrian opposition to come up with a well-articulated political programme to be able to enter into talks with the Syrian government.
"Instead of asking for more assistance of various sorts, the opposition groups, including the National Coalition, should be sticking to their initial offer or expression of readiness to enter a dialogue," he said.
The opposition, he added, "should be amplifying their political programme, because we are not seeing a political programme from them."
On Monday, Russian Foreign Minister Sergei Lavrov hosted Syrian Foreign Minister Walid al-Muallem who for the first time said that Assad's regime was ready for talks with armed rebels.
But the Free Syrian Army's chief of staff Selim Idriss said Assad must step down and "all the killing" should stop before any dialogue could begin.
After talks with US Secretary of State Kerry in Berlin later this week, Lavrov reiterated his call for the Syrian opposition to enter into talks with the Syrian government without any pre-conditions and put together a negotiating team.
Churkin said no outside force would be able to help settle the conflict, which the United Nations estimates has cost at least 70,000 lives, before the warring sides agree to talk to each other.
"Without dialogue, I am afraid, and without the political will on the part of all Syrians, of the main stakeholders in that country, the international community can’t do much. We can’t resolve that crisis for them."