Ukraine's government and pro-Russia rebels have agreed a memorandum on a peace plan for the eastern conflict.
The nine-point deal includes setting up a 30km (19-mile) buffer zone, a ban on overflights of part of eastern Ukraine by military aircraft and the withdrawal of "foreign mercenaries" on both sides.
The agreement was announced at talks in the Belarusian capital Minsk, where a ceasefire was agreed on 5 September.
More than 3,000 have died in fighting in two eastern regions since April.
The original ceasefire has been frequently violated but is still holding.
Ukraine accuses Russia of arming separatists and sending Russian troops to the eastern Donetsk and Luhansk regions. The Kremlin denies it has any role there.
In a separate development on Saturday, three powerful blasts rocked the main rebel-held city of Donetsk, with eyewitnesses saying that a chemical plant may have been hit.
Meanwhile, a humanitarian convoy of about 200 lorries from Russia arrived in the city.
Russia says the convoy - Russia's third in recent weeks - delivered food, water and generators, but this was done without Ukraine's authorisation.
The deal was reached after late-night talks between representatives of Ukraine, Russia, eastern separatists and the Organisation for Security and Cooperation in Europe (OSCE).
Correspondents say it is an effort to add substance to the fragile ceasefire agreement.
Former Ukrainian President Leonid Kuchma, representing Kiev at the talks, said that all sides had agreed to move back some of their heavy weapons.
"Heavy artillery will be moved 15km away from the front line" he said.
He added that the deal would be implemented within 24 hours and monitors from the OSCE would travel to the buffer zone to check for compliance.
Minsk memorandum: Key points
- To pull heavy weaponry 15km by each side from the line of contact, creating a 30km security zone
- To ban offensive operations
- To ban flights by combat aircraft over the security zone
- To set up an OSCE monitoring mission
- To withdraw all foreign mercenaries from the conflict zone
Separatist leader Alexander Zakharchenko said that the two sides did not discuss the status of the rebel-held areas of Luhansk and Donetsk.
"We have our opinion on it while Ukraine has its own," he said.
Earlier this week, Ukraine's parliament passed a bill granting a three-year "self-rule" to parts of the Donetsk and Luhansk regions - a move described as "capitulation" by some Ukrainian lawmakers.
The Russian ambassador to Ukraine, Mikhail Zurabov, representing Moscow at the talks, said that "mercenaries" were fighting on both sides, and called on OSCE to oversee their removal.
Russia has repeatedly said that any of its citizens fighting alongside separatists in Ukraine are doing so in a private capacity.
But Ukraine and the West have accused Russia of actively sending troops and heavy weapons into Ukraine.
There are now fears in Ukraine that Russia wants to create a frozen conflict in eastern Ukraine, the BBC's David Stern in Kiev reports.