Kiev (AFP) - Fighting surged in east Ukraine on Wednesday as Kiev accused pro-Russian forces of launching a "large-scale" attack in breach of a tenuous ceasefire.
Rebels claimed that 15 separatist fighters and civilians were killed as fresh clashes flared, but denied that they had started a new assault.
Medics on the government side told AFP that one civilian had died and five more were wounded. Ukraine's defence minister said seven government troops were injured.
The fighting -- some of the most serious since a shaky European-brokered ceasefire was signed in Minsk in February -- has revived Kiev's fears that the rebels may be readying for an all-out attack.
Ukraine's General Staff said in a statement that rebels started the new offensive close to the rebel bastion Donetsk at 0100 GMT and had unleashed some dozen tanks and up to 1,000 fighters.
The Ukrainian military admitted that government troops fought back against the attack, which was focused on the village of Maryinka, using heavy artillery that was withdrawn under the peace deal.
Ukrainian Defence Minister Stepan Poltorak said the rebels had halted their attack by 3:00 pm (1200 GMT).
Senior rebel commander Eduard Basurin denied that the separatist forces had gone on the offensive, saying the rebels had reacted to defend their people from a "genocide".
- 'Provocative actions' -
Meanwhile the Kremlin -- accused by Kiev and the West of orchestrating the conflict -- lashed out at what it called "provocative actions" by the Ukrainian army.
"In Moscow we are observing and feel acute concern over the provocative actions of the Ukrainian army, which, as far as we can judge, is to a large extent provoking the situation," state news wire TASS quoted Kremlin spokesman Dmitry Peskov as saying.
The State Department in Washington said it was "disturbed by reports" that "combined-Russian separatist forces" had launched fresh attacks.
"Any new attack or aggressive action by combined Russian-separatist forces is unacceptable and contravenes the Minsk agreement," spokeswoman Marie Harf said.
"Russia bears direct responsibility for preventing these attacks and implementing a ceasefire. Any attempts to seize additional Ukrainian territory will be met with increased cost," she said.
Fears in Kiev have swirled in recent weeks that pro-Moscow rebels may use the relative lull in fighting to regroup and prepare for a new offensive to push deeper into Ukraine-controlled territory.
"We don't know the militants' plans," said Ukrainian military spokesman Andriy Lysenko.
"But we do understand that if such activisation has started then there is a clear signal from Moscow."
Russia denies that it is behind the fighting in Ukraine that has killed 6,400 people since last April, and the rebels reject claims they are gearing up to launch a new offensive.
- Checkpoints closed -
A ceasefire was put in place in February after a deal was reached by the leaders of Russia, Ukraine, France and Germany in Minsk, but it remains fragile and fighting has rumbled on around key hotspots.
The United States and European Union have already slapped the toughest sanctions on Moscow since the end of the Cold War due to the crisis.
On Tuesday, Kiev accused Moscow of sabotaging crisis talks after a meeting in Minsk aimed at advancing the peace agreements was postponed to a later date.
A traffic policeman told AFP that all checkpoints to Ukraine from the self-proclaimed Donetsk People's Republic were closed to traffic, with many civilians left stranded because of the shooting.
"We went to Mariupol to buy some food," Inna, who lives near Donetsk, told AFP at one of the checkpoints.
"We've been standing in the sun for several hours now, the military says there are a lot of unexploded shells farther down the road."