Shelling by Syrian government forces of a fuel depot in the opposition-held Idlib region killed three civilians Wednesday and started a huge fire, a war monitor said.

The bombardment struck a building in farmland near the town of Dana used as a supply station for diesel fuel, the Syrian Observatory for Human Rights said.

Large numbers of first responders were attempting to extinguish flames that sent massive plumes of black smoke billowing into the sky, AFP correspondents reported.

The depot is owned by a fuel company affiliated to the authorities in Idlib, who are backed by the Hayat Tahrir al-Sham extremist group, the Britain-based Observatory said.