Russian Foreign Minister Sergei Lavrov said on Tuesday that Moscow was deeply concerned by what he described as ethnic cleansing being carried out by "radical militant groups" in Syria, Reuters reports.
He made his comments after Syrian sources and Russian social media channels reported an apparent attack on one of two military bases Moscow maintains in Syria.
"Radical militant groups are carrying out real ethnic cleansing, mass killings of people based on their nationality and religion," Lavrov said, according to a transcript of his comments published on the Foreign Ministry website.
There was no indication of which groups he was referring to in his speech at a reception marking the last day of the Easter period for Orthodox Christians.
Russia, which maintains two military bases in Syria, has been a key backer of the government of ousted President Bashar al-Assad, who is now in Russia, where he has been granted asylum.
Interim violence erupted in March in the coastal northwest of Syria, which was Assad's stronghold, left hundreds of victims for the former leader's Alawite sect.
Russia has sought to maintain ties with the new Syrian authorities, who have said they may still allow Moscow to retain use of the Hmeimim air base and the Tartus naval base.
Two sources in Syria familiar with the matter said the Hmeimim air base had been attacked earlier on Tuesday.
"Military Informer", a pro-Russian Telegram channel focused on military matters, published a video of a firefight between Russian troops and Syrian fighters at the base.
"Reuters" could not confirm the footage.
Syrian sources said the motive for the attack on the air base, which has been hosting Alawite refugees since the March attacks, was unclear. One of them, a Syrian security official based in the coastal city of Latakia, said an investigation was underway.
This month, US President Donald Trump ordered the lifting of sanctions on Syria imposed during Assad's rule, a major shift in Washington's policy.