Rebel and militant drone attacks on the Hmeimim airbase in Syria used by Damascus ally Russia have increased since last month but all were shot down, the Syrian Observatory for Human Rights said Friday. "Drone attacks against Hmeimim have increased" since July, said the monitor, referring to Russias main military base in the war-torn country, where it intervened on the regimes side in 2015 to help fight the armed opposition. The Britain-based Observatory reported 13 assaults in July and five this month, out of a total of 23 since the start of the year. In such attacks, small unmanned aircraft have been loaded with explosives. But "most of the drones are downed by Russian or Syrian air defenses before reaching their target", Observatory head Rami Abdel Rahman told AFP. The others were also downed. Hmeimim lies just west of rebel and militant-held territory in the northwestern province of Idlib, which the regime head, Bashar al-Assad, has said he intends to bring back under his control. The attackers "are sending a message to Russia that they are able to directly target the main center for Russian forces in Syria", Abdel Rahman told AFP. Hayat Tahrir al-Sham controls more than half of Idlib while a string of rebel outfits hold most of the rest. On Thursday, Russian foreign ministry spokeswoman Maria Zakharova blamed "terrorists" for the attacks, using Damascus and Moscows term for both rebels and militants. "The drone attacks they have launched have become regular in Hmeimim. Our air defenses have downed 45 of them," she said.