AMMAN, Jordan – Clashes spread Saturday between groups nominally united against the Syrian government as mainstream rebels attempted to expel an Al Qaeda-linked group from opposition areas.

Rebels and fighters with the Al Qaeda-linked Islamic State of Iraq and Syria have skirmished in the past but hostilities erupted in large force Friday when the ISIS attempted to seize a rebel base near the city of Aleppo.

As the fighting grew for a second day more groups joined the offensive against ISIS, which at times has fought alongside the rebels and other times against them. The group in turn threatened to withdraw from front lines against government forces if the attacks against them continued and prisoners were not released.

In parts of Aleppo and Idlib province in northern Syria, fighters with the Western-backed Free Syrian Army and Syrian Islamic Front ousted ISIS groups from towns and villages.

“It was a decision to clear the northern suburbs from ISIS,” said Yassin Debo, a spokesman with the Tawheed Brigade, speaking of towns near the Turkish border.

The Mujahedin Army, a newly formed coalition of Free Syrian Army groups, ordered a lockdown for civilians until further notice for several neighborhoods in Aleppo. The activist Aleppo Media Center reported civilian injuries due to the fighting. In other parts of the province protesters turned out against ISIS while others called for an end to fighting between opposition groups.

The clashes also spread as far as Raqqa province in the east, an ISIS stronghold, as well as to the province of Hama to the south.

In a statement, ISIS said the attacks were a conspiracy that came ahead of the planned Jan. 22 Geneva II peace conference, which the group has denounced. Other opposition groups, including the main Syrian National Coalition, have also condemned the international conference orchestrated by the U.S. and Russia and have said they would not attend.

“We call upon the people of Aleppo to take the matter seriously, for the withdrawal of the ISIS from any of those points will mean the invasion of liberated Aleppo and its invasion by the criminal regime,” the statement read.

The other rebels have at times tried to avoid open confrontation with the ISIS, preferring to focus on the battles with government forces.

Muhammad "Abu Zaki” Aassi, a spokesman with the Suqoor al-Sham Brigade in Idlib, said that in the beginning the rebel groups believed ISIS was aligned with their interests against the government of President Bashar Assad.

“But it became clear that they weren’t a part of us,” he said.

“Almost all of the rebels are working together to get rid of these fakers,” Aassi said. “The Syrian revolution hopes that ISIS will leave Syria. Wherever they want to go they can go as long as they leave Syria.”

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Special correspondent Bulos reported from Amman and Times staff writer Abdulrahim from Panama City, Fla.