Huge explosion rocked the village of Qomhana in the central Hama province as rebels and regime forces engage in fierce clashes early Friday.
Local activists said the powerful Islamist alliance of Haya't Tahrir al-Sham, led by former al-Qaeda group Fatha al-Sham, has carried out a suicide bombing attack with tons of explosives that lefts dozens of regime troops killed and wounded.
Rebel groups were focusing their attack Friday on the village of Qomhana, some 8 km (5 miles), north of Ham city, the Syrian Observatory for Human Rights said.
An account on the instant-message service Telegram that is affiliated with the extremist 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.
In support for the Assad army, the Russian warplanes have taken part in airstrikes against rebels to help repel the major attack near Hama, a Syrian military source said Friday.
Rebel groups spearheaded by extremist insurgents launched the attack Tuesday and have captured at least 11 villages and towns, according to the Syrian Observatory for Human Rights, a Britain-based organisation 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.
"Airstrikes 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."
The fighting has underscored the bleak prospects for a new round of U.N.-led peace talks that are underway in Geneva