The UN is looking for a new political solution that would settle the crisis in Syria peacefully and democratically, and Iran could play "a very constructive and helpful" role in helping that process, de Mistura said in a meeting with Iranian Foreign Minister Mohammad Javad Zarif in Tehran on Tuesday.

The UN envoy also put an emphasis on Iran's regional role and clout.

For his part, the top Iranian diplomat highlighted the need for political approaches to end the Syrian crisis.

Zarif also described support for terrorism as the root cause of continued crises and acts of extremism in the region that has caused "instability and humanitarian catastrophe" in crisis-hit countries.

Syria has been gripped by civil war since March 2011 with Takfiri (extremist) terrorists from the ISIL (Islamic State in Iraq and the Levant) currently controlling parts of it, mostly in the east.

More than 220,000 people have been killed in the four-year conflict that has driven 4 million refugees abroad.

In July 2014, UN Secretary General Ban Ki-moon today appointed de Mistura as the special envoy tasked with seeking a peaceful resolution of the conflict in Syria.