Russian warplanes are taking part in air strikes against insurgents to help repel a major attack on Syrian government-held areas near the city of Hama, a Syrian military source said on Friday.
State media later on Friday reported that the army had recaptured all the positions it lost earlier in the week in a rebel assault in the north of the Jobar district of Damascus.
Rebel groups spearheaded by jihadist insurgents launched the attack on Tuesday and have captured at least 11 villages and towns, according to the Syrian Observatory for Human Rights, a Britain-based organization that reports on the war.
It marks the biggest attack by rebels in months. While President Bashar al-Assad still holds the military upper hand in the war, the rebel gains have shown the challenge facing the Syrian army and allied militia as they fight on numerous fronts.
"Air strikes have now started, and there is concentrated artillery firing against the armed groups and the headquarters of their leaders and supply lines, paving the way for the counter-attack," the military source told Reuters. "The Russians are, of course, participating in these raids."
Rebel groups were focusing their attack on Friday on the village of Qomhana, some 8 km (5 miles), north of Hama city, Observatory Director Rami Abdulrahman said.
An account on the instant-message service Telegram that is affiliated with the jihadist alliance spearheading the assault, Tahrir al-Sham, said a suicide attack had been carried out there. The military source said the army had destroyed two car bombs that insurgents had tried to drive towards their positions in Qomhaha, and the attack was thwarted.
The fighting has underscored the bleak prospects for a new round of UN-led peace talks that are underway in Geneva.