Russia warned it will act unilaterally starting on Tuesday to end alleged violations of the "cessation of hostilities" agreement, unless Moscow and Washington urgently reach an agreement to deal with attacks.
The Russian military has accused the United States of dragging its feet on responding to Moscow's proposals on rules for joint monitoring of the Syria ceasefire and response to violations, saying delays are leading to civilian casualties.
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"Further delays with implementing the agreed rules of reaction to violations of the ceasefire regime in Syria are unacceptable," Russia's defence ministry said in a statement.
"Peaceful residents die daily there as a result of provocative actions and shelling."
Lieutenant General Sergei Rudskoi of the Russian General Staff said in a statement on Monday that if the US fails to respond to its proposals on a joint response, the Russian military will have to start unilaterally using force against those who break the truce - starting on Tuesday.
The agreement between the Syrian government and rebel forces has largely held, but there have been a number of alleged violations, including government air raids on opposition areas and the downing of a Syrian air force jet by rebels.
Groups considered to be terrorist organisations by the United Nations - such as al-Nusra Front and the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group - have been excluded from the ceasefire.
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The warning by Moscow came as rebel factions and government representatives continued gathering in Geneva under mediation from the UN in an attempt to bring an end to the five-year-old conflict.
Al Jazeera's James Bays, reporting from Geneva, said the situation at the meeting was "puzzling" as US, Russian and UN officials tried to analyse violations of the cessation of hostilities agreement.
"They [the officials] are saying there have been violations, but there's still been a significant drop in the level of violence," Bays said.
"Most diplomats are telling me a majority of violations have been done by the government side ... so what Russia really is up to here is putting pressure on the US ahead of an important meeting this week in Moscow," he added, referring to a scheduled meeting between US Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov.
"It's clear they're doing a bit of arm-twisting because they want something from Secretary Kerry."
Russia withdrew the bulk of its forces from Syria earlier in March after the ceasefire deal came into effect but still retains a presence in the country.
The country intervened in Syria in September last year, launching air strikes against ISIL and mainstream rebel groups.
Syria marked the fifth anniversary of the war this month at a cost of at least 260,000 dead and a refugee crisis that has seen millions flee the country.
Source: Al Jazeera and agencies