GENEVA (Reuters) - The United States on Monday rejected Russia's call for an urgent meeting over violations of Syria's three-week cessation of hostilities, saying that its concerns were already being handled in a constructive manner.

Russia's general staff of the armed forces proposed on Monday to hold an urgent meeting with U.S. 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.

"We have seen the media reports on alleged Russian concerns over ceasefire violations. Whoever is making such statements must be misinformed, because these issues have been discussed at length already, and continue to be discussed, in a constructive manner," a U.S. official told Reuters in Geneva.

(Reporting by Stephanie Nebehay; Editing by Angus MacSwan)