BEIRUT — Syrian government forces determined to retake the largest opposition holdout in the country’s southwest unleashed an intense bombing campaign, killing at least a dozen people and wounding over 100 in a densely populated town, activists and rescuers said Wednesday.

The aerial bombardment of the town of Nawa came after talks to cede the town failed on Tuesday, triggering the heavy bombardment.

Separately, some 7,000 civilians were expected to be evacuated from two progovernment villages in northwestern Syria as part of a negotiated deal with insurgents who have besieged them for three years.

The Britain-based Syrian Observatory for Human Rights said ‘‘frenzied’’ overnight bombing in Nawa and the town’s surroundings continued into Wednesday, with at least 350 missiles launched. The Observatory said at least 12 people were killed.

Khaled Solh, head of the local Syria Civil Defense known as White Helmets, said they have documented 14 people killed while Nawa’s only hospital was bombed and rendered nonoperational late Tuesday.

The government has stepped up its military offensive on the remaining opposition pockets in the southwestern region, which includes the Daraa and Quneitra provinces that straddle the border with Jordan and the frontier with the Israeli-occupied Golan Heights. In recent days, Syrian forces have turned to the last opposition pockets near the frontier with Israel. Hundreds of civilians were seen taking cover in shelters along the frontier, apparently seeking safety in the demilitarized zone between the two countries.