Syrian rebels from the Islamist Al-Nusra Front on Thursday seized the town of Shadadeh in the oil-rich northeastern province of Hasake, on the border with Iraq, a monitoring group said.

"After three days of fierce battles against the army, Al-Nusra Front fighters have seized control of Shadadeh," said the Syrian Observatory for Human Rights, which relies on a broad network of activists, doctors and lawyers for its reporting.

Fighting and car bomb attacks by the jihadists left more than 100 troops dead in three days, during which 30 Al-Nusra Front fighters also died. Five of the jihadists killed in the violence were from Kuwait, said the Observatory.

"Dozens of employees" working for the state petrol company were also killed in the rebels' assault on the town, said the watchdog, without elaborating.

Elsewhere in the strife-torn country, the army made its own military advance, seizing a key district in the central city of Homs after several weeks of fierce fighting, said the Observatory.

"The army has entered Jobar in western Homs, and rebel fighters have withdrawn from the district," said Observatory director Rami Abdel Rahman.

The victory comes a week after the army took control of Kafraya, also in southwestern Homs.

Activist refer to Homs city as "the capital of the revolution" and several of its districts have been suffocated by a siege for some eight months.

On January 19, the army launched an all-out bid to secure the route linking Damascus to the coast, which runs through western Homs but has so far failed to take complete control.

In violence elsewhere in Homs province, the air force bombarded "for the 10th day in a row" the ancient city of Palmyra, activist Mohammed al-Khatib told AFP via the Internet.

Warplanes also raided the nearby town of Rastan, which has been out of the control of the army for at least a year, said the Observatory.

"Homs province is strategic to the regime because it is the largest in the country and because it links Damascus to the coast," said Abu Rawan, a Rastan-based activists.

"The army will do all it can to take back rebel-controlled territory," he added.

The air force also conducted several raids on rebel-held towns near Damascus, said the watchdog, naming Douma and Saqba among the targets.

The violence came a day after at least 247 people, including 105 civilians, were killed across Syria on Wednesday—one of the highest daily tolls in recent months, the Observatory said.