Syria war: Dozens dead in IS attack on Deir al-Zour
Islamic State militants have launched a fierce assault on government-held areas in the eastern Syrian city of Deir al-Zour, with dozens reportedly killed.
Twelve government soldiers and 20 IS fighters were killed, said the UK-based Syrian Observatory for Human Rights.
At least two civilians were also killed in IS rocket fire on government-controlled parts of the city, it added.
The jihadists have besieged government-held parts of the city, which borders Iraq, since early 2015.
IS already controls half of the city as well as most of the surrounding province, which shares the same name.
Deir al-Zour connects the militant group's de facto "capital" in Syria, Raqqa, to territory it controls in Iraq.
The latest offensive comes amid a continuing ceasefire, brokered by Russia and Turkey last month, between government and rebel forces.
But the truce does not cover IS nor rival jihadist group Jabhat Fateh al-Sham, which was known as al-Nusra Front until it broke off formal ties with al-Qaeda in July.
There are hopes the truce - which has mainly held despite some clashes - will lay the groundwork for peace talks planned for later this month in the Kazakh capital of Astana.
The umbrella group representing Syria's political and opposition factions, the High Negotiations Committee (HNC), voiced its support for the talks on Saturday.
"Concerning the forthcoming meeting in Astana, the (High Negotiations) Committee stresses its support to the military delegation... and expresses hope, that the meeting would reinforce the truce," it said in a statement.
Official invitations have yet to be issued for the Astana talks, but Turkey's Foreign Minister Mevlut Cavusoglu has said Washington will be asked to attend.
The Syrian Observatory for Human Rights (SOHR) said the city of Deir al-Zour had been hit by at least six explosions since Saturday morning.
Syrian government war planes hit back against IS positions, the state-run Sana news agency reported.
Rami Abdel Rahman, who runs the monitoring group, said Saturday's attack by IS was the "most violent" on the city in more than a year.
The jihadists are reportedly trying to cut off the main road linking the airport and the city in a bid to stop the government's supply lines.
Syrian and Russian aircraft have been carrying out regular air drops on the besieged area, where about 200,000 people live.