President Petro Poroshenko said about "200 insurgents used tanks to storm" Novolaspa -- a village halfway between the separatists' de facto capital Donetsk and the Kiev-held port of Mariupol -- in a pre-dawn raid that caught government soldiers off guard.
Chief of Staff General Viktor Muzhenko "informed the president that the Ukrainian forces gave a fitting rebuff and repelled all the attacks," the presidency said.
But the defence ministry later reported the insurgents mounting a second attack on the same village whose outcome was not immediately clear.
"Ignoring the truce agreements, our enemies are continuing to stage provocations that are meant to escalate the conflict," the defence ministry said in a statement.
The Ukrainian foreign ministry called the clashes "a dangerous indication of a further escalation to come".