BEIRUT (AP) — Syrian activists say fierce fighting is underway between pro-government forces and Islamic State militants around a garrison in the eastern city of Deir el-Zour.

Wednesday's fighting came the day after Syrian troops backed by Russia and Iran breached a nearly three-year IS siege of parts of the city near the Iraqi border.

By nightfall, activists said the IS militants had counterattacked with multiple suicide assaults near where the Syrian troops had linked up with government forces inside the city. Heavy fighting was ongoing around the military base of the 137th Brigade on the outskirts of Deir el-Zour.

The breaching of the siege was a victory for President Bashar Assad, and could soon provide relief for tens of thousands of civilians besieged by the militants since early 2015.