The Syrian government, backed by Russian and Iranian military forces, on Saturday escalated its assault on the country’s rebel stronghold, pummeling the northwestern province of Idlib with airstrikes and shellings, according to reports.

Russian war planes conducted about 60 air raids in the region Saturday over the course of three hours, the Telegraph, a British newspaper, reported. The strikes killed four civilians, according to the Syrian Observatory for Human Rights, a British nonprofit organization.