Iran's Foreign Minister Mohammad Javad Zarif visited Damascus on Tuesday ahead of a fresh round of talks next week in Kazakhstan towards ending Syria's eight-year civil war.
Iran and Russia are key allies of the Damascus regime, and along with rebel backer Turkey have sponsored the so-called Astana negotiations track to end the conflict.
Kazakhstan is to host a fresh round of talks on April 25-26 in its capital, last month renamed from Astana to Nur-Sultan.
In Damascus, Zarif and President Bashar al-Assad discussed "the next round of Astana talks and the importance of lasting communication between Damascus and Tehran for continued cooperation", the presidency said in a statement.
Both countries are facing a flurry of sanctions by Western nations including the United States, with Washington this month designating Iran's elite Islamic Revolutionary Guard Corps a terrorist organisation.
Syria is in the grips of a growing fuel crisis that it blames on these sanctions.
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Zarif and Assad accused Western countries headed by the United States of "launching wars and economic terrorism against anyone who did not agree with them" in regional matters, the presidency said.
Earlier on Tuesday, Zarif met his Syrian counterpart Walid Muallem.
After the meeting, Muallem told journalists Iran, Russia and Turkey would be focusing on the jihadist-held bastion of Idlib in northwestern Syria, pro-government newspaper Al-Watan said.
The region on the border with Turkey is held by Syria's former Al-Qaeda affiliate, Hayat Tahrir al-Sham, and is in theory protected from a massive regime offensive by a Russia-Turkey deal.
The September accord aimed to set up a buffer zone around Idlib, but was never fully implemented as jihadists refused to withdraw from it.
"The Astana guarantors... need to abide by the commitments linked to the Idlib file," including "disarming terrorists groups and them leaving Idlib", Muallem said, according to Al-Watan.
Regime forces have continued to bombard Idlib despite the deal, increasingly so in recent weeks.
Zarif is expected to visit Turkey after Damascus.
Endless rounds of UN-backed Syria peace talks have failed to stem the bloodshed, and Iran, Russia and Turkey have sponsored the parallel Astana negotiations track since early 2017.
Tehran has provided steady political, financial and military backing to Assad throughout the war, which has killed more than 370,000 people and displaced millions since 2011.
The Syrian regime has made a military comeback with Russian military support since 2015, and now holds almost two-thirds of the country.