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.
Analysis: BBC business correspondent Theo Leggett
The new sanctions are intended to ramp up economic pressure on Russia. They are designed to make it much harder for state-owned energy and defence companies to borrow money on European financial markets, building on existing measures which target Russian banks.
A ban on selling so-called dual use goods, such as machinery or computing equipment which can be used for both civilian and military purposes is to be extended, while a further 24 people will be added to a list of individuals who are banned from travel within Europe and whose assets in the region are 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”.