Russia says 13 armed drones have recently been used to attack its air base and its naval facility in western Syria.
The Russian Defense Ministry said on January 8 that there were no casualties or damage as a result of the attacks on the Hmeimim air base and Tartus naval facility.
Russian forces were able to overpower radio signals for some of the drones and gain control of them during the attacks overnight on January 5-6, a statement said.
Other drones were destroyed with short-range Pantsir-S1 antiaircraft missile systems, it also said, adding that the unmanned aerial vehicles were carrying foreign, professionally manufactured explosives.
"Engineering solutions used by the terrorists in the attack...could have been obtained only from a country possessing high-tech capabilities for providing satellite navigation and remote control," it added, without naming any country.
A monitoring group, the Britain-based Syrian Observatory for Human Rights, said the attacks were carried out by an Islamist rebel faction that operates in Latakia Province, where the Hmeimim base is located, according to the Associated Press news agency.
Russia has given President Bashar al-Assad's government crucial support throughout Syria's civil war and has long been at odds with U.S. support of certain rebel groups in the Syrian civil war.
The conflict has killed hundreds of thousands of people and driven millions from their homes since it began with a crackdown on pro-democracy protests in 2011.
Also on January 8, the Syrian Observatory for Human Rights said that air strikes by Russian warplanes and shelling attacks by Syrian government forces on rebel-held parts of Idlib Province, northeast of Latakia, enabled the regime forces to advance into 14 villages.
At least 21 people were killed in the aerial bombardment and shelling since January 7, the observatory said.
Idlib is the only province in Syria to be almost entirely controlled by antigovernment forces that are dominated by a coalition of Islamist factions called Hayat Tahrir al-Sham.
The provincial capital, also called Idlib, was late on January 7 the scene of a deadly blast that hit the headquarters of the militant faction Ajnad al-Qawqaz. Many of its fighters are from the Caucasus and Russia.
There has been no claim of responsibility for the bombing that claimed at least 25 lives.
More than 40 Russian military personnel died in Syria since Moscow launched a campaign of air strikes in September 2015, in many cases using Hmeimim as a base.
Russia's Defense Ministry said last week that two Russian service personnel were killed in a mortar attack on Hmeimim on New Year's Eve.
It denied a report by the Kommersant business daily that seven military planes were destroyed in the attack.
The ministry also said that one of its military helicopters crashed in Syria on December 31 due to a "technical malfunction," killing both pilots aboard.
During a visit to the Hmeimim air base on December 11, Russian President Vladimir Putin declared victory over "the most combat-capable international terrorist group" -- a reference to the extremist group Islamic State (IS) -- and announced a partial withdrawal of Russian troops.
Western officials say that the Russian campaign, particularly in its earlier stages, has focused heavily on targeting rebels seeking Assad's ouster rather than IS militants.
Putin said on December 28 that more than 48,000 Russian military personnel had served in the operation in Syria, and that Russia's presence at Hmeimim and Tartus would be "permanent."
On December 29, Putin signed a law ratifying an agreement enabling Russia to expand operations at its naval facility in Tartus.