Nearly 700 killed in Syria rebel infighting

(cnn) -- Nearly 700 people have been killed in nine days of fierce clashes between an al Qaeda affiliate and other Islamist and rebel groups, activists said Sunday.

Forces from the al Qaeda-affiliated Islamic State of Iraq and Syria have increasingly come into conflict with Free Syrian Army fighters and other hard-line factions opposing the Syrian regime, while ISIS attempts to impose its strict form of Islamic Sharia law on areas coming under its control in northern Syria.

In the last nine days, 697 people have been killed in the fighting, activists said.

The victims include 351 combatants from the Islamist and non-Islamist rebel battalions, 246 ISIS fighters, and 100 civilians, the Britain-based Syrian Observatory for Human Rights said.

The activist group said the deaths took place between January 3 and January 12.

Among the 100 civilians killed in the clashes, 21 were executed by ISIS in the children's hospital in Qadi Askar in the northern rebel stronghold of Aleppo, the group said.

CNN cannot independently verify daily death tolls, but the United Nations has said more than 100,000 people have been killed in Syria since 2011.

Uneasy alliance

For months, the groups maintained an uneasy alliance as they fought to topple Syrian President Bashar al-Assad's government.

But now, the infighting has threatened to tip the balance among rebel forces toward militant groups and away from more secular brigades.

In a statement, the opposition Syrian Coalition media office condemned "any and all violations" and said armed gangs were taking advantage of the infighting between ISIS and the Free Syrian Army.

The statement, signed by Syrian Coalition media office director Khalid Saleh, cited these as "illegal practices, intimidating civilians, and theft, taking place all over Syria; particularly in the northern parts of the country."

"We call on FSA brigades to work with civil revolutionary bodies and local councils operating in those areas to address the threat of those gangs, and make sure those gangsters are hunted down and brought to justice," the statement said.

The violence comes as the "Friends of Syria" group of foreign ministers, including U.S. Secretary of State John Kerry, convenes in Paris on Sunday in a last-ditch attempt to convince the Syrian opposition to attend a peace conference in Geneva, Switzerland, at the end of January.

In Iraq, where at least nine people were killed and more than 40 wounded in several car explosions on Sunday, security forces in Mosul said they have detained 137 ISIS suspects in a series of raids in the city over the past seven days.

CNN's Marie-Louise Gumuchian contributed to this report