Syrian rebels launched a major new offensive against forces loyal to President Bashar Assad in the country's northwestern Alawite heartland Sunday, claiming to have overrun a string of villages in the mountains overlooking the coastal port of Latakia.

At least 30 rebel fighters and government loyalists were killed in the fighting, in which the rebels used tanks and heavy artillery to advance to within 20 km of the Assad family's mountain hometown of Qurdaha in the province of Latakia, according to activists and human rights groups.

The claims could not be independently verified.

The push in Latakia comes as the rebels show signs that they are starting to recover from a string of recent setbacks that had triggered concerns among their regional allies that Assad's regime may be poised to crush the 2½-year-old revolt. Rebel commanders and opposition leaders say the concerns appear to have spurred fresh supplies of weapons to the rebels in recent weeks, though it is unclear who is supplying them.

The scale of the offensive, which appeared to be the biggest yet in the Assad family's heartland, will come as a blow to the recent confidence displayed by the regime, said Charles Lister of IHS Jane's Terrorism and Insurgency Center.

Jihadist groups, including the al-Qaida-affiliated Islamic State of Iraq, appear to have taken the lead, with as many as 1,000 fighters, many of them foreigners, from more than 40 rebel units taking part, he said.