Ukraine's military has threatened to use its "entire arsenal" against pro-Russia forces in the restive east, despite a February peace plan forbidding the use of heavy weapons.
"We will use our entire arsenal and all the means at our disposal to beat back the enemy's assault," Ukrainian military spokesman Vladyslav Seleznyov told AFP on Tuesday.
Kiev claims the eastern fighters have launched a fresh missile assault north of government-controlled Mariupol.
"The rebels used to launch Grad missile attacks on rare occasions. Now, it is an everyday occurrence," Seleznyov said, adding, "We cannot risk the lives of our soldiers."
Meanwhile, the pro-Russians blame Kiev for the latest surge in violence along the 500-kilometer (300-mile) frontier.
One of the leaders of the pro-Russia fighters says Kiev's army has fired 500 mortar shells and rockets at the eastern fighters positions since Monday afternoon, killing one fighter and a civilian.
The warring sides signed a peace deal dubbed Minsk II, at a summit in Minsk, in February. The agreement requires both sides to observe the ceasefire and pull out all heavy weapons, among other measures, to reach a final peace deal.
The full implementation of the agreement has been put on ice with neither side pulling back their heavy weapons from the war zone, according to the Organization for Security and Co-operation in Europe (OSCE).
UK minister in Ukraine
Meanwhile, British Defense Secretary Michael Fallon met Ukrainian Prime Minister Arseniy Yatsenyuk in Kiev on Tuesday, reiterating support for the Kiev government.
"The conflict is not settled," Fallon was further quoted as saying by Yatsenyuk's office, adding that the issue remained "red hot."
Fallon is scheduled to conduct an inspection of the British military group deployed to the country to train around 650 Ukrainian soldiers in latest warfare.
There has been an exponential effort on behalf of the United States and NATO to beef up Kiev forces.
Moscow says the West's initiatives in Ukraine are fueling the conflict.
The 16-month clashes have killed nearly 7,000 people and displaced another 1.4 million people.