Ukraine has accused pro-Russian separatists of firing heavy Grad rockets in violation of a ceasefire between the two sides, as seven people were reported injured in fresh clashes.
Russia has also accused Ukraine of violating parts of the Minsk peace deal.
Six Ukrainian soldiers were wounded during fighting over the past 24 hours, Ukrainian army spokesman Andriy Lysenko said, stoking fears of an escalation in violence following a month of relative peace since the signing of the agreement.
The interior ministry also said that a civilian had suffered a shrapnel wound in the government-held town of Dzerzhynsk, after it came under mortar fire late last night.
Mr Lysenko warned that "the situation remained unstable" along the whole conflict line, where rebels had used mortars, grenades and heavy weapons, against the terms of the ceasefire.
The army earlier reported that separatists had fired 120mm mortars in the village of Pisky and used tanks in nearby Opytne, both close to the hotspot of Donetsk Airport.
Ukraine also said its forces repelled an attempt to storm one of their positions in the village of Shyrokyne, close to the strategic port of Mariupol, the largest city still under government control in the conflict zone.
More seriously, they claim that rebels fired heavy Grad rockets on Orikhove, a frontline village north west of separatist stronghold Luhansk.
It is the second time that rebels have been accused of using the multiple rocket launchers since the peace deal came into effect on 15 February.
Under the terms of the ceasefire, the two sides agreed to pull back their heavy arms to create a buffer zone of between 50km and 140km, depending on the range of the weaponry.
Ukraine's interior ministry has said a convoy of military equipment, including ten tanks, had entered the rebel-held town of Gorlivka, 10km north of Donetsk.
Despite the recent lull in fighting that has claimed over 6,000 lives since April, experts from a Ukrainian think-tank warned that a new offensive could be launched "in the coming weeks".
According to the Kiev-based International Centre for Policy Studies, rebels are gathering troops "all across the front line".
Separatist forces currently comprise around 35,000 to 40,000 fighters, including up to 10,000 Russian fighters, it added.
Ukraine's defence ministry yesterday said the near year-long conflict had claimed the lives of 1,750 Ukrainian soldiers.
Meanwhile, Russia has urged Germany and France, which helped negotiate the peace deal, to do more to ensure the Ukrainian government sticks to the agreements that were reached.
"The countries acting as guarantors of the Minsk agreements... Russia, Germany, France... should carry out their share of responsibility for ensuring the provisions are fulfilled," Kremlin spokesman Dmitry Peskov told reporters.
"To ignore that one side is not delivering on the agreements is not conducive to normalising the situation."
Germany's Foreign Minister has said the crisis in Ukraine does not and cannot have a military solution, adding all involved parties must avoid any steps that could led to a new escalation of the situation.
Frank-Walter Steinmeier said, "one thing is clear I think to all of us: there is no, and there cannot be, a military solution to the crisis in Ukraine," after meeting his counterparts from four central European countries in Bratislava.
Mr Steinmeier said he would meet Ukrainian and Russian foreign ministers in Paris on Wednesday to discuss an oversight mechanism for a ceasefire in eastern Ukraine.
Meanwhile, Russia's Deputy Finance Minister Sergei Storchak has said Russie will not request early repayment of debt owed by Ukraine.
In late 2013 Russia acquired €2.8 billion in Ukrainian Eurobonds that fall due this December.
Russia has also said it is considering banning all fruit imports from Serbia amid suspicions the Balkan country was re-exporting Polish apples to Russia.
Russia banned all fruit imports from the European Union as part of a wider range of sanctions introduced last August.
