Fighting is reported to have subsided in eastern Ukraine after the government agreed a ceasefire with pro-Russian rebels.
Ukraine's President Petro Poroshenko confirmed on his Twitter account that a peace plan had been signed, while pro-Russian rebels also announced the news on the social media site.
There were initial reports of shelling in the rebel stronghold of Donetsk moments after the deal came into force at 4pm UK time.
But the area later fell quiet.
Mr Poroshenko, who has been attending a Nato summit in Wales, said the agreement followed a phone conversation with his Russian counterpart Vladimir Putin.
"Human life is the highest value and we must do everything possible and impossible to end the bloodshed and the suffering," said the Ukrainian President.
The United Nations has put the death toll in the five-month conflict at more than 2,600.
Mr Poroshenko said 12 steps, including a decentralisation of powers, the provision of humanitarian aid and the release of prisoners on both sides, had been agreed under the terms of the ceasefire.
The deal was reached after talks between Ukraine and pro-Russian rebels in the Belarussian capital, Minsk. Officials from Russia and the OSCE security watchdog also participated.
The West has accused Russia of sending troops and tanks to participate in the conflict, something Moscow has consistently denied.
European leaders agreed to hit Russia with a fresh round of sanctions on the second and final day of the Nato summit, despite the deal.
The sanctions include credit restrictions on Russian companies, export bans, and travel bans and asset freezes on a new set of officials.
Speaking after the summit, however, Prime Minister David Cameron indicated they may be lifted if the ceasefire inspires a more durable peace deal.
While welcoming the truce, US President Barack Obama admitted there was a degree of pessimism about the chances of lasting peace.
He said he was "hopeful but based on past experience also sceptical that the separatists will follow through and the Russians will stop violating Ukraine's sovereignty and territorial integrity".
Sky's Katie Stallard, who is on eastern city limits of Mariupol, said soldiers from both sides remained in position and that it was difficult to see the ceasefire holding "long term".
"No one has much faith in the ceasefire here," she said.
"There is scepticism about the timing. President Putin has come up with the peace plan right at the point European leaders were preparing to finalise tougher sanctions on Russia.
"What this also doesn't resolve is that we're hearing from the self-proclaimed prime minister of the Lugansk People's Republic, who is saying that this ceasefire doesn't address the status of their 'republic' and they do not abandon their plans to separate from Ukraine."
Meanwhile, Nato announced plans to create a 'Spearhead' rapid response force to counter Russian aggression in Ukraine.
But Moscow said joint military exercises planned by Kiev and Nato in Ukraine - and announced along with the Spearhead force - could undermine peace moves.
Russia's foreign ministry said in a statement that military exercises - planned for September 16-26 - would cause "increased tensions, threaten the tentative progress in the peace process in Ukraine and contribute to the aggravation of a split in the Ukraine society."