The violence comes despite the ceasefire agreement and warnings to Russia it faces additional sanctions if the truce is broken.
At least 11 service personnel have been killed and dozens wounded in the last 24 hours in eastern Ukraine, officials have reported.
It comes despite the ceasefire agreement reached on Thursday, which is due to come into force this weekend.
“In the Donbass, this night was not a calm one. The enemy shelled positions of the ‘anti-terrorist operation’ forces with the same intensity as before,” a statement by the military said.
It said fighting had been particularly intense around Debaltseve, a key railway junction linking the rebel strongholds of Donetsk and Luhansk.
Pro-Russia separatists had used rockets and artillery to attack government forces holding the town, the statement added.
Rebel authorities said three civilians had been killed and five wounded in shelling by government troops on Luhansk.
Another two civilians were killed and six injured on Friday morning when a shell fired by separatists hit a busy cafe in the nearby town of Shchastya, the Kiev-controlled regional administration said.
Russia has been warned sanctions will be stepped up if the truce to end the 10-month Ukraine conflict is not fully implemented.
The ceasefire, which comes into effect on Sunday, was agreed after 16 hours of talks between Russia, Ukraine, France and Germany in the Belarusian capital Minsk.
A previous truce was violated almost immediately by both sides and there are doubts the latest one will hold.
German Chancellor Angela Merkel said the deal provided “a glimmer of hope – no more, no less”.
Russia has already been hit with financial and diplomatic sanctions for allegedly supplying the separatists with heavy weapons and fighters – which it denies.
Mrs Merkel warned: “We hold open the possibility, if these new agreements are not implemented, that we must take further measures.”
European Council President Donald Tusk said previously-agreed sanctions against 19 Russian and Ukrainian individuals and nine entities would still come into force next week.
“Our trust in the goodwill of (Russian) President Putin is limited, this is why we have to maintain our decision on sanctions,” he said.
The terms of the ceasefire include a withdrawal of heavy weapons, Ukraine taking control of its Russian border, the granting of special status to rebel regions and addressing the humanitarian crisis created by the fighting.
Ukrainian President Petro Poroshenko admitted to having doubts, saying: “It was very difficult negotiation and we expect a not easy implementation process.”
The Organisation for Security and Co-operation in Europe has said it plans to send 350 of its observers to eastern Ukraine to ensure the terms of the truce are monitored.
The US described the agreement as “potentially significant”, but also expressed concern about the situation on the ground.
“The United States is particularly concerned about the escalation of fighting today, which is inconsistent with the spirit of the accord,” the White House said in a statement.
More than 5,400 people have died since the conflict began last April.