A sudden surge in clashes between Ukrainian forces and Russian-backed rebels killed at least seven people on Monday despite a tattered truce in Ukraine's war-scarred east.
The overall death toll reported for the past two days rose to 12 after the bloodiest outburst of violence since the former Soviet republic and its foes last month agreed an "indefinite" ceasefire.
The fighting came as Ukrainian President Petro Poroshenko urged German Chancellor Angela Merkel to step up economic sanctions against Moscow, and fears grew in Kiev that US support could wane should President Donald Trump draws closer to Russian leader Vladimir Putin.
"Since Sunday, there have been continuing clashes and heavy attacks on our positions," Ukraine's 72nd army brigade spokeswoman Olena Mokrynchuk told AFP.
The military in Kiev said three of its soldiers had died overnight.
An AFP reporter in the town of Avdiivka near the de facto rebel capital Donetsk saw Kiev troops capture three rebels on Monday. Two of them later died of their wounds.
Electricity has been off since Sunday and water supplies are sporadic in Avdiivka amid the shelling and gunfire.
The separatists also reported two civilians deaths from Ukrainian fire around Donetsk.
The bloodshed put at risk yet another attempt by exasperated mediators to end one of Europe's bloodiest conflicts since the 1990s Balkans wars.
Poroshenko meets Merkel
The violence coincided with Poroshenko's visit to Berlin to meet ally Merkel -- the German leader who along with French President Francois Hollande helped hammer out a 2015 peace deal in the Belarusian capital Minsk that has failed to achieve results.
"We are certain that today we need decisive and united action that can motivate Russia to sit at the negotiating table and fully implement the Minsk agreements -- particularly its security component -- to stop civilians from dying," Poroshenko said in Berlin before entering the meeting.
"We believe that not only should the sanctions be maintained, but they should be intensified as well," he added.
Merkel said she found the situation "worrying" but gave no indication on whether she intended to add to the pressure on Putin.
Ukraine fears that staunch support from the United States could now dry up if Trump makes good on his campaign pledge to improve ties with Moscow.
Ukraine worries that the war in the east will turn into a "frozen conflict" in which the rebels -- and their backers in Moscow -- control the country's former industrial heartland.
The east of Ukraine comprises coal mines and steel mills whose possession is coveted by both sides of the war, which broke out in April 2014.
The clashes started in the Russian-border regions of Donetsk and Lugansk after a February 2014 revolution ousted Ukraine's Moscow-backed leader and put Kiev on a pro-Western course.
The sides have since agreed to a series of temporary ceasefires and an "indefinite" one on December 23, but none have been respected.
The violence had died down considerably until Sunday and it was not immediately clear what provoked the rebel attack.
The conflict has killed nearly 10,000 people -- more than half of them civilians -- and plunged Moscow's relations with the West to a post-Cold War low.
Russia denies backing the insurgents and only admits that "volunteers" and off duty soldiers had entered the war zone of their own free will.