A US push for an immediate ceasefire in Syria has run into Russian opposition ahead of talks aimed at reviving peace negotiations on the conflict.
Russia proposed a 1 March ceasefire, but the US believes Moscow is giving itself and the Syrian regime three weeks to crush rebels, reports quoting Western officials said.
World powers are meeting in Munich later for talks on the Syria conflict.
Discussions come amid fresh warnings of a worsening humanitarian situation.
A surge in fighting in Syria's Aleppo province has displaced about 50,000 people,the International Committee of the Red Cross (ICRC) warned - adding that supply routes for aid had been cut, putting civilians under "enormous pressure".