At least one Ukrainian soldier was killed and four others injured on Tuesday as violence flared-up in eastern Ukraine.
Pro-Russian separatists tried to break through the frontline using 120-millimetre calibre machine guns, according to Ukrainian authorities.
"The rebels and the Russian occupier have organised a cynical provocation in order to make the peace process fail," said Ukrainian president Volodymyr Zelensky said on Facebook.
Zelensky announced that the National Security Council would meet to discuss the issue.
"Our policy to end this war remains unchanged, as well as our resolve to answer to any military attack against Ukraine," the president added.
According to Kiev authorities, Russian separatists on Tuesday morning attacked Ukrainian posts near Novotochkivka and Krymské, less than 10 km away from one of the three areas where they had withdrawn last year.
The Ukrainian forces have been fighting against pro-Russian separatists for six years in a conflict that has killed over 13,000 and displaced 1.5 million people.
The intensity of the battles decreased significantly after the Minsk peace agreements were signed in February 2015, but violence regularly flares-up.
Russia is suspected to support the rebels. Since Zelensky's rise to power in 2019, the relations between the two countries have improved.
Zelensky met with Russian President Vladimir Putin last December at a peace summit in Paris, but the political resolution of the conflict, the last active conflict on European soil, has not progressed.