Islamic State (ISIS) fighters have partly captured Syria's eastern city of Deir Ezzor after a massive assault, killing "around 300 civilians" in an onslaught described by Syria's state news agency SANA as a "massacre" based from reports coming from residents of the city.
If confirmed it would be one of the highest tolls for a single day in Syria's nearly five-year war, the Daily Mail reported.
The ISIS militants have also abducted at least 400 civilians including women and children after capturing a new territory, according to activists from the London-based Syrian Observatory for Human Rights.
"After their attack on Deir Ezzor yesterday, ISIS abducted at least 400 civilians from the residents of the Al-Baghaliyeh suburb it captured and adjacent areas in the northwest of the city," Observatory chief Rami Abdel Rahman said.
"Those abducted, all of whom are Sunnis, include women, children and family members of pro-regime fighters," he added.
They were transported to areas under ISIS control in the west of Deir Ezzor province and to the border with Raqqa province to the northwest.
On Saturday alone, ISIS fighters killed at least 85 civilians and 50 regime forces in Deir Ezzor, the Observatory said.
The ISIS has posted a statement announcing its capture of Deir Ezzor. The jihadi group claimed its forces have gained control over the radio tower, several warehouses and neighbourhoods in the outskirts of the city.
It also claimed that its fighters have killed "dozens" of soldiers loyal to Syrian President Bashar al-Assad.
"The battles are ongoing until now and we ask Allah for victory and consolidation," the ISIS said in its statement.
According to the Observatory, the ISIS has so far gain control of around 60 percent of Deir Ezzor city, capital of the province of the same name in an oil-rich region bordering Iraq.
Sporadic fighting between ISIS and regime forces continued Monday in the northwest of the city, the Observatory said.
Russian warplanes carried out airstrikes in support of Assad's fighters in Al-Baghaliyeh overnight, it said.
The Syrian regime still controls parts of the provincial capital and a nearby military airport despite repeated attacks from ISIS, the Observatory said.
