(CNN) Dozens of people have been killed by a wave of bombardment in Idlib, Syria, according to the White Helmets, a local volunteer search and rescue group. At least 33 people have died since Friday, the group said on Monday.

Syrian President Bashar al-Assad's army, with support from Russian air power, has stepped up its attacks on the northwestern province, the country's last major opposition bastion and home to more than 3 million Syrians.

The government has said that it is targeting terrorists in Idlib. But if the violence continues, hundreds of thousands of civilians could be displaced in the coming weeks, international aid organizations warn.

At least 100,000 people had already been forced to flee their homes in Idlib in the space of just five days, the International Rescue Committee said Monday. It warned that another half a million people could be displaced in the coming weeks.

Rehana Zawar, the IRC's country director for northwest Syria, has urged the UN Security Council to restart negotiations on a cross-border resolution before it is too late.

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