U.N. Special Envoy Staffan de Mistura is struggling to keep negotiations alive after the main opposition High Negotiations Committee (HNC) left formal talks last week due to a surge in violence and stalled aid convoys, despite a two-month truce.
Fighting has intensified in Aleppo province in recent weeks as the partial truce brokered by the United States and Russia has all but broken down.
De Mistura, who will brief the U.N. Security Council on Wednesday, is expected to appeal to major powers to convene urgently a ministerial meeting of the International Syria Support Group (ISSG), diplomats said.
Foreign Minister Sergei Lavrov of Russia, the main backer of Syrian President Bashar al-Assad's government, has so far resisted the idea of a fresh ministerial meeting, they added.
Bashar Ja'afari, head of the Syrian government delegation, spoke briefly to reporters after meeting de Mistura on Tuesday, a day before the two-week round was due to end in Geneva.
"I can describe this particular round as useful and constructive," Ja'afari said, declining to take questions.
Attacks by government forces and rebels killed at least 30 people, including eight children, in the last 24 hours in Aleppo, a monitoring group said.
The ISSG task force on the cessation of hostilities was meeting in Geneva on Tuesday to review the latest violations, diplomats said.
"We are gravely concerned by the increase in breaches of the cessation of hostilities. The regime's relentless bombing of civilians in opposition-controlled areas is clearly threatening the talks," a Western diplomat close to the talks, speaking on condition of anonymity, told Reuters.
"If talks cannot be resumed, there is a severe risk of escalated conflict. This must be avoided. We therefore encourage the ISSG to convene urgently to address the situation."
The Western diplomat voiced disappointment that "Russia has not exerted pressure on the regime to act constructively in Geneva" and implement Security Council resolutions on the ground.
"Russia and Iran should act responsibly and contribute to military de-escalation," he added.
For more details watch full report in the video above