Syrian forces and rebels battled Sunday for a third straight day for control of a key crossing on the northern border with Turkey, the Syrian Observatory for Human Rights said.
"Fighters from (the Al-Qaeda-affiliated) Al-Nusra Front and other groups have attacked the crossing and forced out regime forces and national defence auxiliaries," Observatory chief Rami Abdel Rahman said.
However, he added that fierce fighting was still under way at the Kasab crossing, which was first attacked on Friday.
On Tuesday, Al-Nusra and Islamist groups Sham al-Islam and Ansar al-Sham announced the launch of an offensive dubbed "Anfal" in Latakia province.
The province, which includes President Bashar al-Assad's family village, is considered a regime stronghold, and many residents are from his Alawite minority.
"Significant military reinforcements have been sent to the government forces," said the Observatory, which relies on a network of activists and medical sources on the ground for its reports.
It said that nearly 80 fighters on both sides have been killed since Friday.
On Saturday, the fighting spread to other areas of Latakia province, mainly villages under the control of the regime, which responded with air raids and ambushes, killing at least 20 rebels and wounding 30.
The fighting at Kasab prompted Assad's government to complain to the United Nations that Turkey was providing cover to rebels crossing the border from its territory.
Elsewhere on Saturday, in and around former commercial capital Aleppo in the north, rebels seized a strategic hill overlooking the regime-held west of the city, the Observatory said.
They also briefly cut the road to Aleppo airport.
The Observatory said that among those killed in Saturday's clashes -- which claimed the lives of at least 50 rebels and 26 loyalists -- was the head of the Presidential Guard in Aleppo, Colonel Abbas Samii.
More than 146,000 people have died in Syria's three-year war. Millions more have been displaced.