Russia has proposed a new ceasefire in Syria to begin 1 March, as fighting in the country intensifies leading to a new wave of displacements.
US officials said the proposal has not yet been accepted and there are some reservations with Moscow's plan, Reuters reported.
Russia's Foreign Minister Sergey Lavrov spoke with his US counterpart John Kerry on Wednesday about the situation in Syria.
It comes as world powers are due to meet on Thursday in Munich for a Syria Support Group conference.
Kerry is said to be pressing Russia to adopt a ceasefire plan and for the regime to allow humanitarian aid into Syria, ahead of the meet.
However, a UN source earlier accused Russia of "stringing Kerry along" with the talks, according to Reuters.
"It's clear to everyone now that Russia really doesn't want a negotiated solution but for Assad to win," the diplomatic source told Reuters.
Rebel backers such as Turkey and Saudi Arabia would agree there is every reason for caution.
A similar proposal to Moscow's new offer was made last week.
It ended when Russia launched a massive bombing campaign on rebel-held territories with a sweeping offensive by pro-regime militias on the ground.
The regime managed to capture strategic territory in Aleppo province and southern Syria forcing hundreds thousands in opposition territories to flee their homes to.
Syrian opposition delegates in Geneva for peacetalks last week insisted that peace talks follow US resolution 2254.
This stipulates that the regime must end its blockades on rebel-held territories and for a ceasefire to be implemented.