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, Russia´s foreign minister Sergei 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."
Later, US Secretary of State John Kerry said he was hopeful the cessation of violence could be restored, and he warned Syrian President Bashar al-Assad of consequences if violations continued.
"If Assad does not adhere to this, there will clearly be repercussions, and one of them may be the total destruction of the ceasefire and then go back to war. I don´t think Russia wants that," he told a news conference in Washington.
"If Assad´s strategy is to somehow think he´s going to just carve out Aleppo and carve out a section of the country, I´ve got news for him - this war doesn´t end.
"It is simply physically impossible for Assad to just carve out an area and pretend that he´s somehow going to make it safe, while the underlying issues are unresolved in this war. And as long as Assad is there, the opposition is not going to stop fighting it... one way or the other."
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".
The UN Security Council passed a resolution demanding the protection of hospitals, clinics and health workers in war zones. Secretary General Ban Ki-moon said there was no justification for attacks on medical facilities.
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 55 in an air strike on a hospital the US says was deliberate
On Tuesday, 19 people were killed by rebel rocket fire in government-controlled areas of Aleppo, monitoring group the Syrian Observatory for Human Rights said.
State media said a hospital was hit, killing three people and wounding 17.
The Observatory said 279 civilians had been killed in Aleppo by bombardments since 22 April - 155 in rebel-held areas and 124 in government-held districts.