US Secretary of State Mike Pompeo on Thursday spoke with Russian Foreign Minister Sergey Lavrov over phone to discuss the ongoing challenges in Syria and the US' "serious concerns" related to possible military campaign in Idlib, the US State Department said.

According to a statement issued by State Department spokesperson Heather Nauert, Pompeo asked Lavrov to support efforts in the Organization for the Prohibition of Chemical Weapons (OPCW), as well as efforts "to hold the Syrian regime accountable for its use of chemical weapons."

As the Syrian army is poised for a possible battle on the last major rebel stronghold in the country, the United States, France and Britain on Tuesday warned Syrian President Bashar al-Assad against using chemical weapons, saying that "we remain resolved to act if the Assad regime uses chemical weapons again."

The Syrian Foreign Ministry on Wednesday condemned the tripartite statement as part of "the campaign of threats, hypocrisy, and misinformation resorted to by those powers against the Syrian Arab Republic, which comes in the framework of the outright support to the terrorist groups."

The three Western nations launched a missile attack on Syrian military positions in April, claiming that they had targeted the facilities involved in manufacturing chemical weapons in Syria.

But the Syrian government has repeatedly denied the allegations and said that Western powers were creating excuses to strike Syria and such statements could encourage the rebels to stage such an attack to frame the Syrian army.

While stressing that the Syrian forces have never used chemical weapons, the Syrian Foreign Ministry said the rebels have used chemical weapons under the direct support of Western powers as well as some regional countries such as Turkey, Saudi Arabia and Qatar.

The Western statement came on the fifth anniversary of the alleged chemical attack that took place in the formerly rebel-held Eastern Ghouta, on the outskirts of Damascus in 2013.

(Top image: A general view shows refugee tents erected on the Syrian side of the Israeli-Syrian border as seen from the Israeli-occupied Golan Heights on July 19, 2018. /VCG Photo)