On Sunday, media reports emerged claiming that Russia and Syria were carrying out airstrikes against areas controlled by the so-called moderate opposition factions which had agreed to ceasefire.
"We investigate such reports. I have to tell you that as of today, there is no truth to these reports," Ryabkov told reporters.
"We believe that instead of using unsuitable means to try and blame Russia for the fragility of the current ceasefire, the US-led anti-IS coalition should urge some of its subordinates to be more careful at this time," he added.
Russia and the United States reached an agreement on the ceasefire in Syria on February 22. The ceasefire took effect at midnight on Saturday Damascus time.
The UN Security Council unanimously adopted Resolution 2268 endorsing the Russia-US agreement on the cessation of hostilities in Syria on Friday, shortly before the ceasefire came into force. The cessation of hostilities does not apply to designated terrorist organizations operating in Syria, including Islamic State and the Nusra Front, both outlawed in Russia.
Late on Sunday, Russian top diplomat Sergei Lavrov and US State Secretary John Kerry held a phone conversation calling on media not to broadcast unconfirmed provocative information on Syria ceasefire violations, according to the Russian Foreign Ministry.