Speaking in a televised news conference in Damascus after meeting President Bashar al-Assad and the Syrian foreign minister, envoy Staffan de Mistura said the government's initial response to the proposal "was of interest and constructive interest".
President Bashar Assad had also been quoted on Monday as saying the proposal was worth studying.
De Mistura is pushing an initiative to create truces and improve aid access in defined local areas, starting in Aleppo, once Syria's main commercial hub.
"I believe that the proposal of the U.N. regarding freeze in Aleppo, is a concrete and realistic one," Mistura said.
The state news agency said de Mistura and Foreign Minister Walid al-Moualem agreed to continue consultations on returning stability to Aleppo and easing the passage of humanitarian aid.
Control of Aleppo is divided between an array of armed forces and Syrian army.
In an interview with the British Broadcasting Corporation (BBC), de Mistura said a common threat posed by the “Islamic State” militant group may help push Government and rebel forces toward local truces.
De Mistura told the BBC that ISIS was "destabilising everybody". Asked what incentive rebel and government fighters may have to accept local truces, de Mistura said: "There is one major new factor. What is that called? Daesh. ISIS. Terrorism.
"Saying having a peace plan would be ambitious and delusionary. But I do have, we do have, an action plan. And the action plan starts from the ground: stop the fighting, reduce the violence," he said in the BBC interview.
Syria Freed 11,000 Prisoner in Amnesty
Syria has freed around 11,000 detainees since President Bashar al-Assad declared a general amnesty in June, the country's National Reconciliation Minister Ali Haidar said.
Speaking to AFP in Damascus on Monday, Haidar said "11,000 people have benefitted from the amnesty and been released from prison."
He was referring to a "general amnesty" announced by President Bashar Assad a week after his re-election as president.
Haidar said the figure was rising gradually as the justice ministry, which is in charge of applying the presidential decree, examined prisoner files.
The Syrian government presented the amnesty as the largest since the outbreak of the country's conflict in 2011.
It was also the first to include those accused of crimes under anti-terrorism" law.