BEIRUT (AP) -- Syrian government forces and rebels clashed across the country's north on Sunday in the latest indication that a monthlong cease-fire may be breaking down, as the Islamic State group seized two villages along the Turkish border from other insurgents.
Syrian rebels advanced on government positions in the Turkmen Mountains of the northwest Latakia province, a stronghold of President Bashar Assad, according to the Britain-based Syrian Observatory for Human Rights, which relies on activists inside the country.
It said an insurgent coalition led by the jihadist Ahrar al-Sham, alongside al-Qaida's Syrian affiliate, the Nusra Front, seized the village of Baydaa as heavy fighting continued throughout the day. The Local Coordination Committees, another activist group, confirmed the advance and said nine government soldiers were killed.
The advance builds on a week of heavy fighting around the north of the country that has raised concerns about the durability of a U.S. and Russia brokered "cessation of hostilities" that took effect in late February, bringing relative calm to much of the country. The Nusra Front and the Islamic State group are excluded from the cease-fire.
The Observatory said at least 35 fighters died in clashes Saturday night and early Sunday south of the country's second city, Aleppo, where opposition groups led by the Nusra Front seized the village of al-Ais eight days ago, killing dozens of government troops and allied militants from the Lebanese Hezbollah group.
Syrian Prime Minister Wael Nader al-Halki told a Russian parliamentary delegation that Syrian troops and the Russian air force are preparing a joint operation to retake al-Ais, Russia's TASS news agency reported Sunday.
The IS group has meanwhile launched a major offensive along the Turkish border, seizing two villages near a border town captured by Western-backed rebels two days ago.
IS militants seized Sheikh Reeh and al-Bal on Sunday, the Observatory said.
The extremists exploded seven bombs around Marea and other villages and towns, according to the activist-run Azaz Media Center, based in a northern town of the same name, which called it the fiercest IS offensive in a year.
The IS-linked Aamaq News Agency claims the capture of the two villages and says a suicide operation targeted rebel fighters in opposition-held Kafr Shush.
The Western-backed Free Syrian Army captured the border town of al-Rai from IS on Friday.
Rami Abdurrahman, head of the Observatory, said IS is on the offensive to protect its stronghold in nearby Dabiq. The town has great symbolic importance to the extremists, who believe based on medieval prophecies that it will be the site of a doomsday battle against infidels.
Abdurrahman said fighting is intensifying on all the fronts in Aleppo, adding that it "definitely" threatens the cease-fire.