Russia, Ukraine, the US and the European Union have said that all sides have agreed to steps to “de-escalate” the crisis in eastern Ukraine.
Their foreign ministers were speaking at the end of talks between Russia, Ukraine, the EU and US in the Swiss city of Geneva.
Analysts say the outline agreement could stay economic sanctions the West was preparing to impose on Russia.
Ukraine has been in crisis since its pro-Moscow president was toppled.
Russia then annexed the Crimean peninsula – part of Ukraine but with a Russian-speaking majority population – in a move that provoked international outrage.
This was followed by the seizing of government buildings in eastern Ukraine by pro-Russian separatists opposed to the new order in the capital Kiev.
Following the Geneva talks, Russian Foreign Minister Sergei Lavrov, Ukraine’s Foreign Minister Andriy Deshchytsia, US Secretary of State John Kerry and EU foreign policy chief Catherine Ashton said there was agreement that all illegal military formations in Ukraine must be dissolved, and that everyone occupying buildings must be disarmed and leave them.
They added that there would be an amnesty for all anti-government protesters under the agreement, and talk of “inclusivity” – possibly a suggestion that Russian-speaking areas of Ukraine might be granted more autonomy.
These steps will be overseen by monitors from the Organization for Security and Co-operation in Europe (OSCE).
US President Barack Obama called the deal promising, but said the question remained whether Russia would now use its influence – previously exerted “in a disruptive way” – to restore order in Ukraine.
“I don’t think we can be sure of anything at this point,” he said at a press briefing in Washington on Thursday evening.
“We have put in place additional consequences that we can impose on the Russians if we do not see actual improvement of the situation.”
Mr Lavrov earlier said that long-term constitutional reforms were necessary in Ukraine, but added that all parties involved in the Geneva talks had agreed the crisis needed to be “regulated by Ukrainians themselves”.
The Russian foreign minister also insisted his country had no desire to send troops into Ukraine.
Mr Kerry described the talks as “a good day’s work”, but said words had to be turned into actions and that he would have no choice but to impose tougher sanctions on Russia if Moscow failed to demonstrate that it was serious about lowering tensions in Ukraine.
He said the extent of the crisis had been highlighted in recent days by the “grotesque” sending of notices to Jews in eastern Ukraine, demanding that they register themselves as Jewish.
The notices, which purport to be from the pro-Moscow authorities in Donetsk, have caused alarm in the Jewish community, although their authenticity has not yet been verified.
Mr Kerry also praised the Ukrainian government for the restraint it had shown in the face of what he said was provocation from pro-Moscow elements.
Speaking for the Kiev government, Mr Deshchytsia said: “We disagree with Russia on many things, but what we agreed today is to put an effort, joint efforts, to launch the process of de-escalation in eastern Ukraine. And Russia committed it to be part of this process.
“So it will be a test for Russia, if Russia wants to really show that it is willing to help the stability in these regions.”
Baroness Ashton said the agreement contained “concrete steps that can be implemented immediately”.
But correspondents say the deal has so far had little impact on the ground, with pro-Russian supporters continuing to occupy a local government building in Donetsk.
A protest leader said they would not leave unless pro-European demonstrators in Kiev’s Maidan Square packed up their camp first.
“We’ll see what they do there before we make our decision here,” Alexander Zakharchenko told the Reuters news agency.
Earlier Russian President Vladimir Putin had warned that Ukraine was heading into an “abyss” by confronting pro-Russian separatists in the east of the country.
He said claims that Russian agents were acting in the region were “rubbish”.
He was speaking live on Russian TV in the wake of Wednesday night’s clash in Mariupol, eastern Ukraine, in which three separatists were reportedly killed by Ukrainian security forces after hundreds of pro-Russians attacked a military base.
The clash took place hours after apparently unsuccessful attempts by the Ukrainian military operation to retake territory elsewhere in eastern Ukraine from armed pro-Russian rebels.
In one instance, an armoured column of Ukrainian paratroopers lost control of some of their armoured vehicles to pro-Russian separatists.
Following Wednesday’s events, Ukraine’s State Border Service announced on Thursday that it was “significantly” restricting entry into the country by adult men from Russia because of the risk of “acts of terror”.
Russia and Ukraine have been on a collision course since pro-Moscow Ukrainian President Viktor Yanukovych was toppled in February by supporters of more engagement with the West, in particular the EU.
The US and EU have imposed visa bans and asset freezes on a small number of Russian government officials, but have been considering more serious measures, accusing Moscow of encouraging anti-government elements in Ukraine.
The EU, which depends on Russia for some 30% of its gas supplies, has been discussing the possible impact of economic sanctions with member states.