United Nations Special Envoy for Syria Staffan de Mistura is seen on an electronic screen as he speaks to attendees after a session of the Syrian Congress of National Dialogue in the Black Sea resort of Sochi, Russia January 30, 2018. REUTERS/Sergei Karpukhin

GENEVA (Reuters) - The United Nations Special Envoy Staffan de Mistura renewed his urgent call on Friday for a ceasefire to stop both the “horrific” bombing of besieged eastern Ghouta and indiscriminate mortar shelling on Damascus.

The ceasefire needs to be followed by immediate, unhindered humanitarian access to eastern Ghouta and evacuation of sick and injured, de Mistura said in a statement read out by U.N. spokeswoman Alessandra Vellucci to a Geneva briefing.

The three guarantors of the Astana process - Russia, Iran and Turkey - must meet urgently to re-install the de-escalation zones in Syria, he said, speaking hours before a U.N. Security Council vote on a resolution on a 30-day truce