Russian Foreign Minister Sergei Lavrov says he has submitted a proposal for a ceasefire in Syria, as world powers meet in Munich.
Mr Lavrov gave no further details about the plan, but it is understood to envisage a truce starting on 1 March.
The US is demanding an immediate end to hostilities, as it suspects Russia wants to give Syrian government troops three weeks to crush rebel forces.
Russian air strikes are helping the Syrian army advance in Aleppo province.
The UN High Commissioner for Human Rights, Zeid Raad Al Hussein, wants the world powers to ensure talks in Geneva aimed at finding a political solution to the conflict are reconvened as soon as possible, following their suspension last week.
“The warring parties in Syria are constantly sinking to new depths, without apparently caring in the slightest about the death and destruction they are wreaking across the country,” he said. “It is a grotesque situation.”
More than 250,000 people have died in almost five years of war in Syria. Eleven million others have fled their homes as forces loyal to President Bashar al-Assad and those opposed to his rule battle each other, as well as jihadist militants from so-called Islamic State (IS).
Thursday’s meeting of the International Syria Support Group (ISSG) in Munich will bring together 17 countries, including both allies and opponents of Mr Assad.
Mr Lavrov and US Secretary of State John Kerry met each other before the talks to discuss what the Russian foreign minister described as a “quite specific” ceasefire proposal.
“We will wait for the American response before we take it to the ISSG,” he added.
Moscow has proposed that the ceasefire start on 1 March, but Washington fears that rebel forces might suffer irreversible losses in northern and southern Syria before then, US officials say.
Mr Kerry wants a ceasefire to be effective immediately and accompanied by humanitarian organisations being given full access to the 400,000 people trapped in besieged areas.
The UN human rights chief earlier expressed “utmost alarm” at the rapidly worsening human rights situation in and around the city of Aleppo.