UK-based Syrian Observatory for Human Rights (SOHR) has revealed that Russian forces are building an airstrip near the military airport, Hmaymim airport located in Latakia, Syria.
The monitoring group said that the information was provided to it by 'reliable sources'.
In a statement on its website, SOHR said: "The Russian forces are working on establishing a long runway in Hmaymim Airport area that is able to accommodate large planes.
"The Russians have also prevented both the civil and military authorities to enter to the runway area."
SOHR also added that the Hmaymim Airport has recently witnessed arrival of warplanes loaded with military equipment as well as hundreds of Russian military advisers, experts and technicians.
Last week, Greece was said to be considering closure of its airspace to Russian planes carrying material to Syria, following a request from the US.
Russia has been operating regular services to Latakia to bring home Russians wanting to leave Syria.
US Secretary of State John Kerry told his Russian counterpart Sergei Lavrov that stepped-up military support to Syria could further escalate the war in that country, reported Reuters.
According to SOHR, the Russian authorities were working on expanding the agricultural airport of al- Hasmidiyya located in the south of Tartous province.
Additionally, the group said that the Russian experts were working on a study to establish long runways in the International Airport of Damascus.
Hmaymim airport is a government-controlled airport in Syria that is officially named the Basel al-Assad International airport.