BEIRUT (Reuters) - Aerial bombardment by the Syrian army in northwest Syria, the biggest remaining rebel-held enclave, killed at least 28 people on Thursday, a war monitor said.

Warplanes and helicopters struck in Idlib, Hama and Aleppo provinces, including in the towns of Saraqeb and Kafr Nabouda, said the war monitor, the Britain-based Syrian Observatory for Human Rights.

The Syrian army and its allies are pushing toward Saraqeb from Abu Duhur, an airbase they captured last month, and they seized several villages on Thursday, the Observatory said.

The strongest rebel group in northwest Syria is Tahrir al-Sham, an alliance of jihadist factions including a former al Qaeda affiliate previously known as the Nusra Front.

In Damascus, shelling by rebel groups killed seven people and wounded 13 others in the government-held Ash al-Warour district, state news agency SANA reported.

The government has pushed rebels from many of the areas they seized during the civil war, which began in 2011, but opposition groups still hold significant pockets near Damascus and Homs and in the southwest, as well as the enclave in the northwest.