Hundreds of people have died after Islamic State (Isis) militants carried out a deadly attack on the government-held eastern Syrian city of Deir al-Zour, around 452km from capital Damascus. The death toll, however, could not be verified as conflicting reports are emerging from the area.

Syria's state news agency Sana reported that around 300 civilians were killed in the IS (Daesh) attack that began on 16 January. "The Daesh (IS) terrorists carried out a massacre in Al-Baghaliyeh, claiming the lives of around 300 civilians, most of them women, children and elderly people," the news agency said, according to Agence France Presse.

"Legal and moral responsibility for this barbaric and cowardly massacre... lies on the shoulders of all the states that support terrorism and that fund and arm takfiri (Sunni extremist)," Syrian Prime Minister Wael al-Halaqi said. According to UK-based Syrian Observatory for Human Rights (SOHR), at least 135 people, mostly Syrian soldiers were killed in al-Baghaliyeh district of the city.

SOHR's chief, Rami Abdelrahman said that fighting between the militants and government forces was ongoing. Meanwhile, Reuters reported that the terror group had killed at least 250 people in Al-Baghaliyeh and Ayash districts of the city. IS also beheaded some of the victims, the news cited sources as saying.

However, Lebanon-based Al-Mayadeen TV claimed that 280 people were massacred and that IS members "threw their bodies in the Euphrates River". Around 400 civilians have been taken hostage, it reported.

According to Syria's Local Coordination Committees (LCC), the deadly attack began at dawn on 16 January, when an IS car bomb exploded in the city, followed by a ground offensive.

SOHR said that Russia – an ally of Syrian President Bashar al-Assad – has been carrying out air strikes to repel IS militants from the area, while government troops are using heavy artillery to push back the terror group.