UKRAINE’S generals warned they have run out of reserves to halt Russia’s shock assault on Kharkiv.
It comes as Vladimir Putin masses more than half a million troops on the frontline in a bid to overpower Ukraine's forces.
Ukraine's military has admitted it is struggling to contain the advance in the north east of the country.
General Kyrylo Budanov, boss of Kyiv’s military intelligence said: “I’ve used everything we have.
“Unfortunately, we don’t have anyone else in the reserves.”
Putin’s troops have seized miles of ground in their fastest advances in months.
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The blitz, said to be the first stage of Russia’s summer offensive, is designed to stretch Ukraine’s already outnumbered defenders.
Kyiv said the Russian push appeared to have run out of steam last night — but, in the face of Putin’s 500,000-strong force, warned that could change quickly.
Royal United Services Institute war expert Dr Jack Watling said unless Ukraine could muster more troops its prospects were bleak as Russia had “significant numerical superiority”.
He said: "The Russian forces have now expanded to 510,000 troops.
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"The outlook for Ukraine is bleak. Its allies must replenish stockpiles."
Ukraine cannot blitz Russian forces massing just over the border because the US has forbidden it from using its weapons such as Himars rockets in enemy territory.
Former UK joint chief General Sir Richard Barrons said that had allowed the Russians to be able to “form up at leisure”.
He added: “Those are the only weapons that will break up Russian forces as they organise themselves for an offensive.”
But desperately needed weapons from the latest US aid package have begun arriving at the front line.
In Kyiv today, Ukraine President Volodymyr Zelensky met US Secretary of State Antony Blinken, who vowed to make Russia pay to rebuild his country.
He said: “It’s what international law demands.”
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RUSSIA massed tens of thousands of troops and tanks and launched a major new ground offensive on northeastern Ukraine on Friday and has seized miles on ground quickly.
The blitz, said to be the first stage of Russia’s summer offensive, is designed to stretch Ukraine’s already outnumbered defenders.
Kyiv said the Russian push appeared to have run out of steam last night — but, in the face of Putin’s 500,000-strong force, warned that could change quickly.
UK defence secretary Grant Shapps said the world is taking its "eye off the ball" after the recent Russian attacks.
Despite the success, Ukraine said Russia has suffered record losses with 1,740 reportedly killed in a single day as its troops are thrown into the Kharkiv meatgrinder assaults.
Thousands of Ukrainian people have also been made to flee their homes out of fear of attacks.
As children have been seen going to school in underground, missile proof bunkers in the heart of war-torn Ukraine.
Russia stepped up attacks on Kharkiv in March targeting energy infrastructure and settlements with constant airstrikes in what analysts predicted were preparations for a new offensive.
The city of Kharkiv, located on the eastern front only 30 miles from the Russian border, was the prime target of Russia's aerial bombardment.
Its mayor had warned the West that it risked being turned into a "second Aleppo" - the Syrian city which heavy Russian bombing helped to decimate a decade ago.
Russia kicked off a new brutal offensive in Kharkiv in northeastern Ukraine days ago.
Close to 40,000 soldiers and 500 tanks were initially massed along the border ahead of the large-scale ground attack Kyiv had feared was coming for weeks.
Heavy fighting has been raging this week, forcing 6,000 residents to evacuate while Ukraine rushes in reinforcements to shore up its stretched defences.
Ukrainian soldiers said the Kremlin is using the tried-and-tested Russian tactic of launching human wave attacks - throwing its troops into meatgrinder assaults for gain territory at high cost.
Dr Alan Mendoza, executive director of the UK-based think tank Henry Jackson Society, told The Sun: "It is a very dangerous offensive in the Kharkiv region right now, the Russians have made significant gains in in a very short time."
Ukrainian forces have now started deploying kamikaze drones in an attempt to push back Russia's swelling army.
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Meanwhile, overnight Ukraine launched a major aerial attack on the Russian-held port city of Sevastopol in occupied Crimea.
Kyiv also launched blitzes on several Russian regions across Belgorod, Kursk and Bryansk using 10 long-range US-supplied missiles known as ATACMS.
Ex-general says there are three key ways Ukraine can win the war
SPEAKING on The Sun's new World at War show, former Joint Forces chief Richard Barrons said Ukraine must strike Russian heartlands, mobilise more troops and the West must keep pumping in the weapons.
General Barrons said that if he was in charge of Ukraine's army the first thing he would be doing was "demanding, not asking" to fire Western weapons at Russian military targets.
Ukraine cannot blitz Russian forces just over the border as they amass for the new offensive because the US has forbidden it from using its weapons on enemy territory.
General Barrons fundamentally disagreed with America's objections to such strikes.
"Russian forces [gather] at leisure just 30 miles from places like Kharkiv," he told The Sun's World at War show which you can watch on and .
US weapons like HIMARS rocket systems are "the only weapons that will break up Russian forces as they organise themselves for an offence," Barrons said.
The retired general also argued that Ukraine needed to sort out its manpower issues.
"Nobody else is going to send their sons and daughters to fight for them. They've got to find more people," he argued.
Barrons also advocated for a constant supply of weapons from the West.
The F-16s and new glide bombs are likely to make a difference, he said. But there's no one "magical weapon", he said, but they are needed in "balance and strength".