Militants in Syria fired four rockets towards Russia's Hmeymim air base in Syria, but all the rockets were destroyed, the RIA news agency cited Russia's Defence Ministry as saying on Thursday.
Syrian government troops on Wednesday morning also repelled three big attacks by militants in Syria's Idlib province, the Russian Ministry of Defence said.
It said in a statement that 500 Nusra front militants, seven tanks, and about 30 pickups mounted with heavy machine guns had taken part in the attacks. The latest clashes mark the biggest escalation since last summer between Assad and his rebel enemies in Idlib province and a belt of territory around it.
The ministry said that Syrian militants based in Idlib had also launched a missile attack on Russia's Hmeymim air base on Wednesday, but that their missiles were either shot down or did not reach their target.
Syrian activists and rebels say opposition fighters have recaptured a village on the edge of their stronghold in northwestern Syria.
Naji al-Mustafa, a spokesman for armed factions, says the fighters regained control of Kfar Nabuda on Wednesday in an overnight counteroffensive, driving government forces from areas they captured earlier this month. Government forces had seized Kfar Nabuda on May 8, cutting into rebel-held territory.
A ceasefire is needed in Syria's Idlib province where there has been a recent upsurge in violence, and the United States is working towards halting the clashes, which have put tremendous pressure on civilians there, U.S. envoy James Jeffrey said on Wednesday.
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THOUSANDS FLEE, HUNDREDS DIE
More than 200,000 people have now fled the violence since the end of April, the United Nations said, and are in urgent need of food and protection.
The Union of Medical Care and Relief Organisations (UOSSM), which provides assistance to health facilities, said the number of displaced this month had spiked to more than 300,000.
Most of the displaced have sought refuge along the border with Turkey, the UOSSM said, with camps springing up in the shadow of the frontier wall.
However, 44,000 people have moved to the regional capital Idlib and another 50,000 have gone to Maarat al-Numan, another large town where the Observatory said an air strike on a marketplace killed 12 people on Tuesday night.
The bombardment has used both conventional air strikes by war planes and "barrel bombs" - improvised explosives dropped by helicopter - according to the Observatory and rescue services.
Since the end of April, there have been 20 attacks on healthcare facilities and one on an ambulance, the United Nations said, putting 19 facilities that serve at least 200,000 people out of action. Some were hit more than once, it said.
The Observatory said 669 people have been killed since the end of April, 209 of them civilians. The UOSSM said 229 civilians had been killed in that period.
Rebels fighting on the mountainous western edge of the enclave said on Sunday that the army had shelled them with poison gas, leading some to suffer choking symptoms.
The U.S. State Department warned it would respond "quickly and appropriately" if that was proven.
However, U.S. Syria envoy James Jeffrey said on Wednesday that Washington did not have confirmation that poison had been used. Rebels said they had not documented the attack because they were under bombardment when it occurred.
Syria's government denies using chemical weapons.