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Hussein Malla, Associated Press
An Assyrian woman wears her community's flag as a headband during a protest with several hundred people in solidarity with Christians abducted in Syria and Iraq, in downtown Beirut, Lebanon Saturday, Feb. 28, 2015. The Islamic State group, which has repeatedly targeted religious minorities in Syria and Iraq, abducted more than 220 Assyrians this week in northeastern Syria.

BEIRUT — Syria's al-Qaida affiliate overran bases belonging to a Western-backed rebel group near the northern city of Aleppo after heavy clashes that killed at least 20 fighters, activists said Saturday.

The fighting took place near the town of Atarib some 30 kilometers (18 miles) west of Aleppo, and pitted the al-Qaida-linked Nusra Front against the mainstream Hazm Movement, which has received support from the United States.

The Britain-based Syrian Observatory for Human Rights said Nusra Front fighters seized control of several Hazm bases. At least 29 Hazm fighters and six Nusra Front militants were killed in the clashes, it said.

An Aleppo-based activist who goes by the name Abu al-Hassan confirmed the clashes, but put the death toll at around 20 Hazm fighters. He didn't have any information on Nusra casualties.

Abu al-Hassan said by telephone that the two groups have had "numerous disagreements" in recent weeks.

In November, the Nusra Front expelled a once-powerful mainstream rebel group from Syria's northern Idlib province. The al-Qaida group frequently cooperates with more-moderate rebel factions, but has turned more hard-line since the U.S. targeted Nusra Front fighters with airstrikes.

South of the capital, Damascus, government troops and their allies took control of several towns and villages on Saturday, the SANA state news agency and the Observatory said.

The takeover of Habaria, Kherbet Sultana, Hamreet and Tal Qrein is part of an offensive the Syrian military and fighters from the Lebanese militant Hezbollah group launched this month that aims to drive back rebels who have pushed closer to Damascus.

The region south of the capital — near the Jordanian border and Israeli-controlled Golan Heights — is also one of the last bastions of mainstream rebels.

In Beirut, hundreds of Syrian Christians protested Saturday outside the local United Nations office, demanding the safe return of more than 220 of their brethren kidnapped this week by the Islamic State group. There has been no word on their fate.

"All we're asking is freedom for our people," demonstrator Faez Hermes Eshaya said. "All my life, we never felt that Muslims were our enemies."