Clashes have been mainly taking place between militants from the so-called Islamic State of Iraq and the Levant (ISIL) and their rival militants over the past 10 days.
The latest battles have occurred in the northern parts of Syria. The so-called Syrian Observatory for Human Rights, which relies heavily on a network of spies working for the foreign-sponsored opposition, said on Tuesday that militants from the ISIL seized the northern Syrian city of Raqqah following days of clashes with rival Takfiri groups.
The ISIL has been battling a coalition of foreign-backed militants in areas across northern Syria.
Earlier this week, the al-Qaeda-linked group seized the town of Bab in the northern province of Aleppo from rival militant groups.
A British defense study showed last year that about 100,000 militants, fragmented into 1,000 groups, were fighting in Syria against the government and people.
Syria has been gripped by a deadly conflict since 2011, with western powers and their regional allies - especially Qatar, Saudi Arabia and Turkey -supporting the militants operating inside the country.
According to the UN report, more than 100,000 people have been killed and a total of 7.8 million others displaced due to the violence.
NTJ/BA