A senior Russian official said Russia's air base in the coastal province of Latakia came under fire from the insurgents, the latest assault on the military post since Friday.
Gen. Viktor Kupchishin said the base was targeted twice Monday by "multiple missile launcher systems." He blamed the attack on al-Qaida-linked Hayat Tahrir al-Sham, the group in control of most of the rebel-held enclave. He said 36 missiles were fired using a drone but were repelled by the defense system. There were no casualties or damage, he said.
Kupchishin said the situation has "deteriorated dramatically" in the area. His comments were carried by Russia's state-owned Tass news agency.
U.N. Secretary-General Antonio Guterres expressed great concern at the intensifying hostilities in what was supposed to be a de-escalation area and alarm at reports of aerial attacks on population centers and civilian infrastructure "resulting in hundreds of civilian dead and injured and over 150,000 newly displaced persons," U.N. spokesman Stephane Dujarric said.
Guterres called for an urgent de-escalating as the Muslim holy month of Ramadan begins, and he urged all parties to recommit to cease-fire arrangements agreed to last September, Dujarric said.
Insurgents in Idlib and Hama provinces, where the rebel-held enclave is located, have previously used drones to target the base. Most of those attacks were thwarted, but they often serve to ratchet up tensions in the area.
Earlier Monday, the government-controlled Syrian Central Military Media said the village of al-Bani and the nearby Othman hill in the northern countryside of Hama province had been captured by Syrian troops.
The Britain-based Syrian Observatory for Human Rights, an opposition-linked war monitor, confirmed that al-Bani had been captured and that troops were marching toward the hill. The Observatory said the intense fighting on Monday killed 20 people.
Jaish al-Ezzat, one of the main rebel groups in the rebel-held enclave Syria, said it destroyed a Syrian army tank and that all the soldiers inside were killed. The group described "fierce clashes" near al-Bani.
The latest round of fighting has killed dozens and displaced tens of thousands in Idlib and nearby rebel-held areas, who fled to safer regions further north. It's the worst violence since September, when Russia and Turkey negotiated the cease-fire to avert a government offensive on Idlib and surrounding areas.
The Observatory reported more than 60 Russian airstrikes on insurgents Monday alone.
Syria's state news agency SANA reported that Syrian troops intensified their shelling of insurgents in northern parts of Hama province and the southern parts of Idlib.