Iran has accused the US of ratcheting up tensions in the Middle East after Washington claims the Syrian government may be preparing for a chemical attack.

Iranian Foreign Minister Mohammad Javad Zarif made the remarks on his official twitter account on Tuesday. "Another dangerous US escalation in Syria on fake pretext will only serve ISIS (Daesh), precisely when it's being wiped out by Iraqi and Syrian people," he said.

On Monday, US Press Secretary Sean Spicer claimed that the US had “identified potential preparations” for an attack “that would likely result in the mass murder of civilians, including innocent children.”

He added that Syrian President Bashar al-Assad and the Syrian military would “pay a heavy price” if they went ahead with the alleged plan.

The Pentagon claims that it has seen activities linked with chemical weapons at Shayrat airfield in Homs province that was hit by American missiles in April.

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Washington’s accusations were made as the Syrian and Iraqi armies continued to make sweeping gains on their paths to fully liberating the countries from the presence of the Daesh terror group.

Meanwhile, Syria has denied US allegations, saying it has never used chemical weapons in its war against foreign-backed terrorist groups.

Russia has also dismissed the warning by the US that the Syrian government is making "preparations" for a new chemical attack, saying such allegations are unacceptable. “Such threats to Syria's legitimate leaders are unacceptable," said Kremlin spokesman Dmitry Peskov.