Eighteen Ukrainian servicemen have been killed and 54 injured in fresh fighting with separatist rebels, a military spokesman said on Wednesday.
The spokesman, Andriy Lysenko, said government forces had clashed with separatists 25 times in parts of eastern Ukraine near the Russian border in the 24 hours up to Wednesday morning as they continued to squeeze rebel positions.
Ukrainian forces, he said, had again been shelled from inside Russian territory while Ukrainian frontier guards near the border town of Luhansk had come under a four-hour mortar and artillery attack.
"In the past 24 hours, 18 service personnel have been killed in battle and 54 have been wounded," he told journalists, saying casualties had been sustained in several different incidents in the east.
Government troops have been battling the rebels since April in the Russian-speaking east in a conflict which the United Nations High Commissioner for Human Rights says has cost the lives of more than 1,100 people, including government forces, rebels and civilians.
The new overnight deaths among government forces suggests that Kiev military losses now total around 400.
Ukraine and its Western allies accuse Russia of orchestrating the revolt and arming the rebels – something denied by Moscow. The United States and the European Union have imposed sanctions on Russia.
Fighting has intensified since the shooting down of a Malaysian airliner last month, killing all 298 people on board – an act the West laid at the door of the rebels. Russia and the rebels blame the disaster on Kiev's military offensive.
Residents in Donetsk, east Ukraine's main industrial hub and now the main redoubt of the rebels, said Ukrainian warplanes had carried out air strikes overnight.
One resident, who gave only her first name of Svetlana, said: "It was terrible. It was the most powerful strike we have had. The walls of the apartment shook when it [the missile] struck the market and the bus stop next to it".
Lysenko, questioned over the reports, denied that Ukrainian planes had carried out air strikes on the town of nearly one million and said the only Ukrainian plane near the town had been an aircraft providing communications support for troops on the ground.
"The Ukrainian military does not bomb the towns of Donetsk and Luhansk or any other similar populated places," he said.
Russia amassing forces
Russia has amassed around 20,000 combat-ready troops on Ukraine's eastern border and could use the pretext of a humanitarian or peace-keeping mission to invade, NATO said on Wednesday.
Stating the conflict in Ukraine was fuelled by Russia, NATO said in a statement that the troop build-up had further escalated "a dangerous situation."
"We're not going to guess what's on Russia's mind, but we can see what Russia is doing on the ground – and that is of great concern. Russia has amassed around 20,000 combat-ready troops on Ukraine's eastern border," NATO spokeswoman Oana Lungescu said in an emailed statement.
NATO was concerned that Moscow could use "the pretext of a humanitarian or peace-keeping mission as an excuse to send troops into Eastern Ukraine," she said.
Moscow denies Western accusations that it has armed and supported rebels who are fighting Ukrainian forces in eastern Ukraine. It announced new military exercises to take place all this week, involving bombers and warplanes on Monday in a show of strength near the border with Ukraine.
Polish Prime Minister Donald Tusk said on Wednesday the threat of a direct intervention by Russia's military in Ukraine has risen over the last couple of days.
NATO said early this year that Russia had amassed some 40,000 troops close to the Ukraine border. By June, the number had dropped to less than 1,000, but then Russia started building the force up again.
A NATO military officer, speaking on condition of anonymity, said that early this month Russia had significantly increased the number of troops near the Russian border.
The roughly 20,000-strong troop presence included tanks, infantry, artillery, air defence systems, as well as logistics troops, special forces, and various aircraft, the officer said.
Previously, Russia has used military exercises as cover for intervention, military analysts say.
The European Union and the United States last week agreed tough new sanctions against Russia over its actions in Ukraine, marking a new phase in the biggest confrontation between Moscow and the West since the Cold War.
The conflict worsened dramatically after the downing of Malaysian flight MH17 over rebel-held territory on July 17 by what Western countries say was a Russian-supplied missile.
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