Islamic State (Isis) have launched their biggest attack in Syria for months, monitors and state media have said.

Dozens of people have been killed and several more are wounded after several rockets were fired into the government-controlled city of Deir Ez-Zour on Saturday (14 January).

IS (Daesh) terrorists reportedly attacked military posts in villages near the Deir ez-Zour airport, but Syrian warplanes hit back, destroying one tank and three vehicles.

Three people were killed and nine were wounded in the area, Syria's state media Sana said.

In the fighting that ensued, the British-based Syrian Observatory for Human Rights said at least 12 Syrian Arab Army forces and 20 IS terrorists were killed.

The fighting comes as Syrian opposition on Saturday agreed to participate in peace talks in the Kazakh capital of Astana. IS will not be part of any negotiating process.

Deir ez-Zour province is the target of intense fighting in Syria as the province links IS's de facto capital Raqqa with territory controlled by the militant group in Iraq.

The area was at the centre of controversy after US-coalition airstrikes killed 62 Syrian soldiers and wounded more than 100, days after a ceasefire was agreed.

Deir ez-Zour airport was then immediately overran by IS, which provoked angry statements from Syria and Russia, which claimed the US was materially supporting the terror network.

Following the attack, President Bashar al-Assad said: "It was a premeditated attack by the American forces because Isis was shrinking."

"It wasn't by coincidence because the raid continued more than one hour, and they came many times," he added.

During the attack, a hotline between Russia and US forces was reportedly left unattended for 27 minutes. In the one hour period, at least 32 strikes were carried out and 380 rounds of 30mm ammunition were fired.

Following a six-week investigation by US Central Command, US Air Force Brigadier General Richard Coe said the attack was a "mistake" but stopped short of apologising to the Syrian government.

"We made an unintentional, regrettable error, based on several factors in the targeting process," Coe said.

Assad has called for the attack to be investigated as a war crime.