Russia has vowed to respond if the European Union imposes new sanctions over the Ukraine crisis.
The EU says the sanctions, targeting more Russian individuals, will come in on Monday but could be suspended if Russia withdraws troops from east Ukraine and observes a current truce.
The ceasefire, agreed in Belarus on Friday, appears to be largely holding.
Some 2,600 people have died since a pro-Russian rebellion began in eastern Ukraine in April.
The Russian foreign ministry said in a statement: “As for the new list of sanctions from the European Union, if they are passed, there will undoubtedly be a reaction from our side.”
The fresh sanctions would add another 24 people to the list of people barred from entering the EU and whose assets have been frozen.
The Russian foreign ministry said the EU was “practically sending a signal of direct support to the ‘party of war’ in Kiev”.
Its statement added: “Instead of feverishly searching for ways to hurt the economies of its own countries and Russia, the European Union would do better to work on supporting the economic revival of the Donbass (eastern Ukraine) region.”
There were no reports of major fighting in the east overnight.
The BBC’s Richard Galpin in Donetsk said he had not heard any of the heavy artillery barrages that took place before the truce while the BBC’s Fergal Keane tweeted from Mariupol, further south, that the ceasefire was holding there.
Ukraine’s National Guard Commander Stepan Poltorak told the Interfax news agency: “As of this morning there haven’t been any violations.”
A BBC crew that travelled to Donetsk airport on Saturday morning heard a few gunshots and small explosions but residents said the night had been quiet.
However, the rebel leader of the self-proclaimed Donetsk People’s Republic, Aleksandr Zakharchenko, said the truce was “not being fully observed”.
Under the terms of the ceasefire, both sides pledge to withdraw heavy weapons from the eastern battlefields as soon as possible.
Russia also agreed with Ukraine to restart humanitarian assistance to the eastern region.
Ukrainian President Petro Poroshenko said the deal was based on a 12-point peace plan that included the release of “hostages”.
He said there should also be talks about a long-term solution to the conflict.
Ukrainian forces had until recently been making gains against the rebels but in the past few weeks the pro-Russian fighters have struck back.
Ukraine and the West reported military columns crossing from the Russian border.