BEIRUT — Islamic State militants launched their biggest assault in a year on government-held areas of the contested city of Deir el-Zour Saturday, attacking from several fronts and triggering intense fighting in the eastern region bordering Iraq, the Syrian government and opposition activists said.

Syrian state TV said three people were killed and nine were wounded in Islamic State rocket attacks on several neighborhoods of the city.

Intense fighting broke out between Syrian troops and the extremist group’s fighters both inside the city and around the vicinity of a nearby military airport controlled by government forces. The militants had launched their multipronged attack starting from the area of Baghaliyeh near the northwestern tip of the city. Deir el-Zour carries strategic significance for the Islamic State as it links the group’s Iraq territory to its de facto capital of Raqqa in Syria.

Loud explosions that shook the city were reported. Activists said Syrian warplanes were taking part in the battles.

The Deir Ezzor 24 news network reported ongoing clashes since the morning near Deir el-Zour military airport and other fronts in the city and said Syrian warplanes targeted Baghaliyeh and Ayash areas and the vicinity of an army base known as Brigade 137 west of the city.

The extremist group, which controls most of Deir el-Zour province, has kept the provincial capital under siege since 2014. Government forces have withstood the encirclement thanks to air-dropped humanitarian assistance and weapons and ammunition flown into the airport.

Remaining residents have reported malnourishment and starvation amid severe shortages of food, water, and fuel.

The Islamic State has tried to capture the government-held neighborhoods of Deir el-Zour and the city’s suburbs over the past months without much success.

The Syrian Observatory for Human Rights said Saturday’s offensive was the most intense since January 2016, when the group killed dozens of people, most of them progovernment militiamen, in wide-scale attacks on the city that saw the group make significant advances.