The Syrian army denied Russian ground troops are fighting alongside its forces, saying Moscow was deploying only air power in Syria.
In a statement issued late on Tuesday on the Syrian news agency SANA, a military source was quoted as saying that reports Russian combat forces were engaged in ground operations were "baseless and mere propaganda".
Russia's three-week-old military operations were limited to aerial bombing of what the Syrian source described as terrorist hideouts, command centers, and weapons depots.
The Syrian statement comes after reports at least three Russians fighting alongside Syrian government forces were killed and several more wounded when a shell hit their position in the coastal province of Latakia.
A pro-government source, who is familiar with military events in Syria, said that at least 20 Russians were at the post in the Nabi Younis area when the shell struck.
The three deaths which occurred on Monday night would be the first known incidence of Russians being killed in Syria since Moscow began air strikes in support of President Bashar al-Assad on September 30.
Rami Abdulrahman, head of the Syrian Observatory for Human Rights which monitors the conflict, told Reuters that his sources in the area had confirmed the deaths of Russians, but did not have a figure. He said he believed they were not regular Russian forces but volunteers.
RIA news agency quoted the Russian embassy in Damascus as saying it had no information about the reported deaths and Russia's Defense Ministry denied that Russians had died recently in Syria.
The Kremlin has said it is not undertaking any steps to recruit and deploy volunteer fighters.
Meanwhile, Syrian president Bashar Assad traveled to Moscow in his first known trip abroad since war broke out in Syria in 2011, meeting his strongest ally, Russian leader Vladimir Putin.
When asked about Assad's visit to Moscow, Turkish Prime Minister Ahmet Davutoglu said, "What can I say. If only he [Assad] would stay longer in Moscow so the Syrian people can be at ease, or if only he could stay there permanently and a real transition period could begin."
NATO member Turkey has long been one of Assad's fiercest critics, insisting that no lasting peace can be achieved in Syria without his removal from power.
"We think the Syrian government has no legitimacy left and our thoughts on this subject have not changed ...There must be a transition in Syria which secures Assad's departure," Davutoglu added.
(Reuters reporting by Suleiman Al-Khalidi, Alexander Winning in Moscow; Editing by Gareth Jones)