Syrian forces shelled the battered city of Homs for another day Monday, striking a makeshift clinic and killing at least 17 people in a mounting toll that has made the city the epicenter of the 11-month Syrian uprising, opposition groups said.

The city, Syria’s third-largest, has emerged as an arena of some of the revolt’s worst violence, with scores dead there in just the past few days.

The bloodshed on Monday followed an onslaught this weekend, when opposition groups said Syrian forces shelled Khaldiya and other neighborhoods for several hours Friday and Saturday, killing more than 200 people in one of the deadliest days of the revolt.

The government has flatly denied the tolls quoted by opposition groups. On Saturday, it said Homs was quiet. State-run media blamed the violence Monday on “armed terrorist groups” firing mortars within Homs, an opposition stronghold.

Explosions could be heard over the phone when speaking with residents. Videos smuggled out by activists showed a dramatic scene at a clinic, as people rushed past doctors and medical staff, shouting, “Oh God.” In one video, purporting to document the scene, blood smeared the sidewalk outside. Another showed bloodied corpses.

Two opposition groups put the death toll at 17.

“People can’t leave their homes,” said Omar Shakir, an activist in the city. “Where can they go? It’s the government’s punishment. It’s revenge.”