Destruction in Deir Ezzor
Destruction in Deir EzzorReuters

The Islamic State (ISIS) group on Saturday launched one of its fiercest assaults yet on the besieged Syrian city of Deir Ezzor, leaving more than 30 regime fighters and jihadists dead, AFP reports.

The attack came as the political opposition said it "supported" upcoming peace talks in the Kazakh capital Astana.

The negotiations will attempt to bring an end to the nearly six-year war by building on a fragile truce agreement, brokered by Turkey and Russia but which excludes jihadist groups such as ISIS.

In Saturday’s wave of suicide attacks, rockets, and tunnel bombs, ISIS killed at least 12 government forces and two civilians in Deir Ezzor, the Syrian Observatory for Human Rights told AFP.

The British-based monitoring group said 20 jihadists were killed in fierce air raids by Syrian and allied warplanes on the city, where around 200,000 people have lived under ISIS siege since early 2015.

ISIS has sought to overrun the entire city, including the key nearby military airport.

Observatory head Rami Abdel Rahman told AFP the attack was the "most violent" assault mounted by ISIS on the city in more than a year.

"Daesh is amassing its forces to attack Deir Ezzor and breach government lines," a Syrian military source told the news agency, using the Arabic acronym for ISIS.

He added that jihadists had aimed to cut the route between the airport and the city, but that the government's counter-attack had stopped ISIS.

ISIS, which controls of most of the province, has launched several attacks in the region over the past two years.

Last year, it kidnapped and shortly afterwards released some 400 civilians in Deir Ezzor.

AFP contributed to this report.