"With every victory on the ground, some Western countries raise their voices and intensify their activities in an effort to change the trajectory of events," said Assad.
"These voices, and any possible actions, will only contribute to further destabilisation in the region," he said in comments posted on the Syrian presidency's social media accounts.
Assad and Velayati criticised Western threats to carry out strikes on Syria in response to the alleged use of toxic weapons at the weekend, the presidency said.
"The threats of some Western countries to attack Syria is based on lies that these countries fabricated along with terrorist organisations," Assad's office said. Syrian troops have braced for Western strikes across the country, hiding assets and deserting key buildings.
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