Pro-Russian separatists in eastern Ukraine have marched dozens of captured government soldiers through the city of Donetsk.
The incident came as Ukraine said it would spend $3bn (£1.8bn) on re-equipping the army to fight the rebels.
President Petro Poroshenko made the announcement ahead of a military parade to mark Independence Day in Kiev.
More than 2,000 people have died in recent months in fighting between government forces and the separatists.
Some 330,000 have fled their homes because of the unrest in eastern Ukraine.
The violence erupted when pro-Russian separatists in the Donetsk and Luhansk regions declared independence from Kiev, after Russia annexed the Crimean peninsula from Ukraine in March.
‘Constant military threat’
On Sunday, the rebels force-marched Ukrainians soldiers through the centre of Donetsk.
Crowds lined the streets chanting “fascists” as the dishevelled-looking prisoners walked by. Some people threw bottles at the captives, Reuters news agency reports.
Donetsk has been the scene of the heaviest fighting since the conflict began.
Ukraine’s defence ministry condemned the parading of captured Ukrainian soldiers.
“The organisers of this disgusting event cannot be considered human,” a spokesman told Interfax-Ukraine news agency. “Nothing is holy” for them, he added.
The BBC’s David Stern: “A very patriotic feel in the capital right now”
In the capital Kiev, President Poroshenko warned that a “constant military threat will hang over Ukraine” for the foreseeable future.
He said the $3bn investment would be spread out over two years, from 2015-2017.
“The events of the last months have for us turned into a real war, albeit an undeclared one,” Mr Poroshenko said in a televised speech on Sunday.
“Over the last six months, a new Ukrainian army has been born in heavy and exhausting fighting.”
Celebrations were also under way in other Ukrainian cities, including Sloviansk
Meanwhile heavy fighting continued between government forces and separatists near Donetsk on Sunday
The military parade featured hundreds of marching servicemen and military hardware. Some critics called the event inappropriate because Ukraine was at war.
A naval parade is also being held in the port of Odessa.
These are the first military parades since 2009, when the previous pro-Russian president, Viktor Yanukovych, abolished them.
Prayers were said and wreaths laid for those who fought on the Ukrainian government side, including those killed during protests against Mr Yanukovych in Kiev last winter.
Separately, security officials quoted by Ukrainian media said that five people accused of planning attacks on bases for pro-government volunteers in the Kiev area, timed to coincide with the celebrations, had been arrested.
Sunday’s celebrations come a a day after the German chancellor, Angela Merkel visited Kiev and met President Petro Poroshenko
The chancellor and the president met as lorries from an unauthorised Russian aid convoy into the east crossed back over the border to return to Russia
Russia has been accused by Nato of amassing troops and tanks near its border with Ukraine
On Saturday, Germany urged both sides to strive for a new ceasefire, warning that Russia could face new sanctions over its alleged interference in Ukraine.
Meanwhile, lorries from an unauthorised Russian aid convoy which had crossed into eastern Ukraine returned to Russia.
Western officials fear the trucks may have held military equipment to help the rebels, but Russia said they had delivered generators, food and drinks.
Key negotiations between President Poroshenko, Russian President Vladimir Putin and EU officials are due to take place in Minsk on Tuesday.
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