The current round of what has become known as the ‘Astana talks’ ¬between the Syrian conflict parties and led by Russia, Turkey and Iran, kicked off on Wednesday, but, according to media reports, the Syrian opposition side walked out of the meeting, citing a new barrage of airstrikes in the area they hold.

“The United Nations is very concerned at the reports of escalation in Syria, including, allegedly, reports of air strikes, particularly in this delicate moment in the Astana discussions where actually proposals to de-escalate the conflict are under very serious discussion,” the UN Special Envoy for Syria, Staffan de Mistura, told reporters, following the suspension of the meeting.

“We are calling, therefore, for the immediate investigation and for immediate institution of measures to ensure that now no strikes are taking place and are halted,” de Mistura said, urging all participants in Astana to “press ahead on Thursday with de-escalation discussions and confidence-building measures.”

Asked if he is confident that the opposition will come back on Thursday, he said that there have been “some incidents produced by one side or the other,” but the important thing is “to make sure that those incidents stop but also do not kill the opportunity for good news related to that.”

Positive outcomes from the Astana talks – which aim to bolster the ceasefire regime brokered by Russia, Turkey and Iran in late December 2016 – would help de Mistura with his role of facilitating the intra-Syrian talks in Geneva, the latest round of which wrapped up in late March. The discussions are guided by UN Security Council resolution 2254 (2015), focusing on matters of governance, a schedule and process to draft a new constitution and the holding of elections as the basis for a Syrian-led, Syrian-owned process to end the conflict.