The U.N. is due to vote Friday morning on a resolution calling for an urgent halt to Syria’s bombardment of the rebel enclave Eastern Ghouta, but Russia said Thursday it would not support the current draft and dismissed “rumors” of high civilian deaths.

As diplomats scrambled to agree to a ceasefire in the assault that has claimed at least 416 lives since Sunday night, Russia’s envoy to the U.N., Vassily Nebenzia, dismissed the widespread media reports of high civilian casualties as “rumors” that were the product of a “mass psychosis.”

“The mass psychosis in global media outlets acting in coordination, disseminating the same rumours in recent days, in no way does anything to help improve understanding of this situation,” he said.

Nebenzia told an emergency Security Council meeting Thursday that Moscow would not support the ceasefire resolution in its present form, calling it unrealistic and saying that the Security Council could not simply impose a ceasefire without consulting the parties on the ground.

Russian Foreign Minister Sergei Lavrov said the draft resolution – which currently excludes ISIS and al-Qaeda affiliate al-Nusra Front from any ceasefire – to also exclude other groups cooperating with them, potentially including the two major rebel groups in Eastern Ghouta, Jaish al-Islam and its rival Faylaq al-Rahman.

The 15-member Security Council is due to vote on the resolution, drafted by Sweden and Kuwait, at 11 a.m. ET Friday. The resolution can be blocked with a veto from any of the five permanent members of the council, including Russia, which has used its veto to shield its ally Syria from U.N. moves against it on at least 10 occasions in the past.

Western diplomats have accused Russia of objecting to the ceasefire to buy more time for Syria, as its forces pound the rebel-controlled pocket of Eastern Ghouta in advance of an anticipated ground assault to retake the territory completely.

Syrian forces attacked the district, containing an estimated 400,000 trapped residents, with air and artillery fire for the sixth straight day Friday, pounding civilian targets including marketplaces and hospitals, according to residents and aid groups. Humanitarian groups warn of catastrophic conditions in the territory, where there are acute shortages of food and medicine due to the regime siege.

Eastern Ghouta, the former bread basket of Damascus situated about 9 miles east of the Syrian capital, is under the control of Islamist rebel groups. The Syrian military denies targeting civilians there, describing its offensive as aimed at terrorists who have fired on civilian areas in Damascus.