MOSCOW, April 5 (Xinhua) -- The Russian Defense Ministry said on Wednesday that the deadly gas contamination in Syria's northwestern province of Idlib was caused by the explosion of chemical weapons produced by the rebels.

Media reports said about 70 people were killed with 200 others wounded Tuesday in a toxic gas attack by Syrian warplanes on the rebel-held town of Khan Sheikhoun.

Syrian air force delivered a strike on the eastern outskirts of Khan Sheikhoun against a large ammunition depot and a cluster of military equipment belonging to terrorists, Russian Defense Ministry spokesman Igor Konashenkov said in a statement.

"On the territory of this depot, there were workshops for the production of land mines stuffed with poisonous substances," he said.

Konashenkov said terrorists used chemical weapons from this depot in Iraq and the Syrian city of Aleppo.

On Tuesday, U.S. Secretary of State Rex Tillerson urged Russia and Iran to exercise influence on Syria to prevent further chemical attacks in the war-torn country.

White House Spokesman Sean Spicer said the United States condemns the gas attack against innocent civilians as "heinous actions" by the Syrian government.

The Syrian Foreign Ministry said Tuesday that the Syrian army did not possess any kind of chemical weapons.

The UN Security Council will hold an emergency meeting later on Wednesday to discuss the suspected chemical attack in Syria.