Beirut (AFP) - Syrian troops backed by Hezbollah fighters on Sunday pressed a counteroffensive against rebels near President Bashar al-Assad's coastal heartland, a monitoring group said.

The Syrian Observatory for Human Rights said that more than 100 fighters have been killed in three days of intense clashes in the Sahl al-Ghab region of central Hama province.

The area borders the Latakia province, a bastion of support for Assad and home to his ancestral village.

A rebel alliance including Al-Qaeda's Syria affiliate, Al-Nusra Front, launched an offensive late Monday against Sahl al-Ghab, in a push threatening a string of pro-regime Alawite villages.

The rebel alliance, Army of Conquest, seized more than a dozen strategic hilltops and other positions, including a power plant, before being pushed out by pro-government forces, said the Observatory.

"In the past three days, the army has been able to take back nearly 50 percent of the areas it had lost," said Rami Abdel Rahman, director of the Britain-based monitor.

The 72 hours of clashes killed at least 73 rebels and 42 regime forces, including Hezbollah fighters and members of the National Defence Forces militia allied with the government, he told AFP.

On Sunday, regime aircraft conducted air raids on rebel positions while on the ground the two sides traded heavy rocker fire and mortar rounds, Abdel Rahman said.

Sahl al-Ghab also borders the province of Idlib to the northwest, a vast majority of which is under the control of the Army of Conquest.

The Alawite sect, an offshoot of Shiite Islam, is the faith to which Assad adheres.