BEIRUT — Syrian activists say government forces have carried out multiple airstrikes on rebel strongholds in the country's north, causing a number of casualties.

They say Tuesday's strikes were concentrated in Idlib and Aleppo provinces, where rebels fighting to topple President Assad have made advances in the past week.

An activist in the northern province of Idlib and the Syrian Observatory for Human Rights said the airstrikes were some of the worst since rebels took over the key city of Maaret al-Numan in Idlib earlier this month. It lies along the main highway connecting Aleppo with the cities to the south, including Homs and the capital Damascus.

Activists reported several casualties from the airstrikes. They say another two people died in artillery shelling of the town of Kfarnebel in the Idlib countryside.