Russia will act unilaterally against those militants who violate ceasefire in Syria if Moscow does not reach agreement with the US on a mechanism of detecting and preventing truce breaches, Russia's Foreign Ministry said on Monday.

The ceasefire agreement, worked out by Russia and the US, is largely respected, the ministry said.

But the two nations, which co-chair the Syria International Support Group, have so far failed to agree on terms of preventing all cases of ceasefire violations, which sends a wrong signal to "those members of the opposition ... who have not dissociated themselves clearly enough from well-known terrorist groups", it said.

Russia's general staff of the armed forces proposed earlier on Monday to hold an urgent meeting with US representatives to agree on the mechanism of controlling the ceasefire in Syria, saying it would act unilaterally starting from March 22 if it gets no response.

The US later rejected the call from Russia's military, saying that its concerns were already being handled in a constructive manner.-Reuters