MOSCOW, May 24 (Xinhua) -- The Russian Defense Ministry on Friday denied a U.S. allegation that the Syrian army had carried out a chemical attack in the Idlib de-escalation zone in northwest Syria.

The only "sources" and "eyewitnesses" of the alleged chemical attack are the terrorists of the al-Qaida-linked Nusra Front, the ministry's spokesman Igor Konashenkov said in a statement.

He said that on May 18, the Syrian government forces unilaterally ceased fire in the region and did not respond to numerous provocations for several days.

Therefore, there were no "attacks" on May 19 in the Idlib de-escalation zone, he added.

"All attempts by the U.S. Department of State to invent another story about 'chemical attacks' are nothing more than a political cover for desperate attempts by terrorists to destabilize the situation in the Idlib de-escalation zone and provoke a humanitarian catastrophe there," Konashenkov said.

The U.S. Department of State said in a statement Tuesday that the government of Syrian President Bashar al-Assad may be renewing its use of chemical weapons, including an alleged chlorine attack in northwest Syria on the morning of May 19.