Russia's foreign minister says a unilateral truce declared by the Syrian military could be extended to the city of Aleppo "in the next few hours".
Sergei Lavrov said Russia was working with the UN and US to include Aleppo in the "regime of calm" that has covered Damascus and Latakia since Saturday.
But Mr Lavrov warned that rebels would have to leave areas where allied jihadist militants were being targeted.
More than 250 people have been killed in Aleppo in the past 10 days.
About two-thirds of those deaths have been in the rebel-held eastern side of the city, including 50 in an air strike on a hospital the US says was deliberate.
On Tuesday, 14 people were killed by rebel rocket fire in government-controlled areas of Aleppo, including three in an attack on a hospital, state media reported.
The UN special envoy to Syria, Staffan de Mistura, travelled to Moscow on Tuesday to discuss efforts to urgently rescue the nationwide cessation of hostilities in Syria, which the US and Russia negotiated at the end of February.
After holding talks with the Italian-Swedish diplomat, Mr Lavrov told reporters that he expected a decision on including Aleppo in the separate regime of calm "in the very near future — maybe in the next few hours".
The unilateral truce had been effect in Latakia and the eastern Ghouta region around Damascus since the weekend thanks to the efforts of the Russian and US militaries, he said.
The aim of Russian, US and UN negotiators was to extend the regime of calm and "ideally make it indefinite", Mr Lavrov added.
He said a joint US-Russian ceasefire monitoring system being set up in Geneva would help to track events on the ground.
But he also warned that so-called moderate rebel groups in Aleppo had to leave areas where militants from al-Nusra Front, an al-Qaeda affiliate that is excluded from the cessation of hostilities, were being targeted.
Mr de Mistura said he hoped that by extending local truces, the cessation of hostilities could be reinvigorated and stalled peace talks in Geneva might resume.
"We all hope that… in a few hours we can relaunch the cessation of hostilities. If we can do this, we will be back on the right track."
He added: "If, as we all hope, there will be definite confirmation that even Aleppo will return to a ceasefire regime, we can imagine that we can restart [peace] talks at the same time."
The US and the Syrian opposition have dismissed Russia's assertion that Syrian government forces are only targeting al-Nusra and accused them of indiscriminate attacks on civilians.
The International Committee of the Red Cross (ICRC) warned last week that Aleppo was being "pushed further to the brink of humanitarian disaster".
Large parts of the city have been destroyed and its infrastructure has been severely damaged, leaving civilians without water and electricity for months.
The partial halt in fighting raised hopes that tentative peace talks in Geneva might bring forward a solution to Syria's bloody five-year civil war.
But the truce all but collapsed after renewed violence, particularly in Aleppo.