By BASSEM MROUE, Associated Press

BEIRUT (AP) — A Kurdish-led fighting alliance on Wednesday captured a hill overlooking a main road in Aleppo from the militant Nusra Front group and its allies, in a surprise offensive aimed at encircling the northern city, Syrian opposition activists and state media said.

In southern Syria, a car bomb targeted a meeting of commanders of a U.S.-backed moderate rebel group, killing 18, including the faction's top commander. Dozens were wounded in the blast in Quneitra province.

The predominantly Kurdish U.S-backed Syrian Democratic Forces' offensive most likely does not break the cease-fire that came into effect five days ago, because Nusra Front and Islamic State group are excluded from the agreement.

Syrian troops and the SDF had halted their offensive in northern Syria for days after the Russia and U.S.-brokered cease-fire began midnight Friday.

Syrian state TV reported that pro-government gunmen captured Castello hill, "cutting supply lines for terrorists" in eastern neighborhoods of Aleppo with southern parts of Aleppo province.

Sami al-Raj, an Aleppo-based opposition activist, confirmed the SDF advances via Skype, saying they are now very close to the road.

Kurdish forces have remained mostly neutral during Syria's five year civil war, but have occasionally clashed with insurgent groups and are the most effective fighting force battling IS on the ground.

An opposition activist based in Turkey said the SDF's apparent aim is to push north of the Aleppo neighborhood of Sheikh Maqsoud and reach government forces in the nearby town of Handarat, which would completely besiege the eastern neighborhoods of the city that are under rebel control. He spoke on condition of anonymity fearing retaliation.

The Britain-based Syrian Observatory for Human Rights reported fighting between Kurdish fighters and militants near Sheikh Maqsoud. It added that militants shelled the predominantly Kurdish Sheikh Maqsoud neighborhood, wounding nearly 20 people.

A siege on rebel-held areas of Aleppo, Syria's largest city and once commercial center, would mark one of the biggest opposition setbacks since Syria's war began in March 2011. Aleppo has been carved into government- and opposition-held sectors since mid-2012.

In southern Syria, opposition activists said a car bomb has killed at least 18 rebels, including the commander of a U.S.-backed armed opposition group.

The Observatory said the car bomb exploded Wednesday afternoon in the southern village of Asheh in Quneitra province, killing at least 18 fighters, including four commanders.

A Quneitra-based opposition activist who goes by the name of Abu Omar al-Golani said that 20 fighters were killed in the blast, among them the commander of the Syria Revolutionaries Front, Capt. Abu Hamza al-Naimi.

He said the blast went off when several commanders were meeting at the group's office in Asheh.

The Syria Revolutionaries Front is a moderate rebel group that was mostly crushed in northern Syria in late 2014 by al-Qaida's Syrian branch, known as the Nusra Front.

An opposition activist, who spoke on condition of anonymity because he was not authorized to leak secret information, said the rebel faction was planning to attack Nusra Front in southern Syria.

No one has claimed responsibility for the blast, which caused widespread damage in the area.

An amateur video posted online by opposition activists showed several bodies in the back of a pickup truck in a road full of debris. Smoke billowed from the area, close to a damaged one-story house.

The video appeared genuine and corresponded with other Associated Press reporting of the events.

In neighboring Lebanon, thousands of supporters of the militant Hezbollah group attended the funeral of senior military commander Ali Fayyad who was killed while fighting against IS in Aleppo province last week. The funeral was held in Fayyad's southern hometown of Ansar.