'A full-scale battle in Syria’s Idlib province will create a humanitarian nightmare unlike any seen in this blood-soaked conflict,' Guterres tweeted on Wednesday.
'My message to all parties: Protect civilians. Preserve hospitals. Respect international humanitarian law,' he added.
He went to on to say that 'fighting terrorism does not absolve warring parties of their core obligations under international law.'
Iranian President Hassan Rouhani, Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan in the final statement of Tehran summit, released on September 7, emphasized their strong and continued commitment to the sovereignty, independence, unity and territorial integrity of the Syrian Arab Republic as well as to the purposes and principles of the UN Charter and highlighted that they should be respected by all.
Tehran summit was held while the Syrian army is preparing to liberate the last major stronghold of terrorist groups in Idlib in northwestern Syria.
In the meantime Iranian Foreign Minister Mohammad Javad Zarif in a Twitter message said 'as @realDonaldTrump destroys US credibility & humiliates his 'allies' with 'little games', we're delighted to engage with responsible powers today in Tehran to further move towards political solution in #Syria. Agreed to work to end terrorism & avoid human suffering in #Idlib.'