The Syrian military unleashed heavy airstrikes and artillery bombardments targeting rebel strongholds in the north on Tuesday, killing at least 90 people, according to activists.

The barrage came as the U.N. food agency warned that more and more Syrians are depending on assistance from the World Food Program to stay alive with the civil war worsening. The airstrikes hit northern Idlib and Aleppo provinces, both bordering Turkey.

Rami Abdul-Rahman, who heads the Britain-based activist group Syrian Observatory for Human Rights, said the airstrikes were "concentrated and intensive" and the worst in weeks. He said warplanes carried out 12 raids in the area of Maaret al-Numan in one hour. The group relies on a network of activists on the ground.

Activists say that more than 33,000 people have died in the Syrian conflict, which began in March 2011 as a peaceful uprising against Assad's regime but morphed into a civil war.

ASSOCIATED PRESS