BEIRUT  - At least 27 Syrians were killed in violence on Friday, opposition activists said, only four days before a troop pullback agreed by President Bashar Assad as part of a peace plan proposed by mediator Kofi Annan.

The Syrian Observatory for Human Rights said shelling had killed at least 10 people, including four rebel fighters, in the flashpoint central city of Homs. Two soldiers killed in separate clashes and one person was killed in the town of Douma, it said.

The British-based Observatory, using its network of contacts in Syria, also reported seven civilians and four soldiers killed in clashes and bombardments in Anadan, north of Aleppo. The fresh violence erupted a day after UN Secretary-General Ban Ki-moon said the conflict was worsening and attacks on civilian areas persisted, despite assurances from Damascus that its troops had begun withdrawing under the peace plan.

In the latest violence, activists reported tank fire in at least three urban centers on Friday - the town of Douma near Damascus, the restive city of Homs and Rastan, north of Homs.

“At least 5 tanks and 10 buses loaded with security men and Shabiha (pro-Assad militia) entered Douma,” one local activist said. “There has been shelling on Douma since the morning. In Rastan, an activist said Free Syrian Army rebels had confronted a morning tank thrust. “They blocked the advance and the Assad army left. Then artillery started,” he said.

Anti-Assad demonstrations broke out after Friday prayers in the eastern province of Hasakeh, in the town of Qamishli and Deir Al-Zor city, activists said. Protesters carried the white and green rebel flag. Some saluted other rebel cities. Army shelling of villages in the northwestern province of Idlib has prompted a swelling exodus of refugees. Turkey said there were now 23,835 Syrian refugees on its territory. Over 2,800 arrived on Thursday alone, a Turkish official said, more than double the highest previous one-day total.

They crossed near the Turkish village of Bukulmez and more were waiting to do so, the official said. Forty-four minibuses ferried the arrivals to a refugee camp at Reyhanli.