The defence minister’s remarks are a rallying cry – rather than a concrete plan – as Russia pounds cities.
Ukraine plans a “million-strong army” equipped with Nato weapons to retake the south of the country from occupying Russians, the defence minister says.
Retaking the areas around the Black Sea coast was vital to the country’s economy, Oleksii Reznikov said.
However, the comments are more of a rallying cry than a concrete plan, says the BBC’s Joe Inwood in Kyiv.
The defence minister’s remarks come as Russia makes progress in taking territory in the eastern Donbas region.
An attack on a block of flats on Sunday killed at least 18 people – with more than 20 are feared buried under rubble.
Rescuers are still looking for survivors at the site of the five-storey building in Chasiv Yar, near the city of Kramatorsk, in Donetsk region which has been the focus of a Russian push.
In his interview with The Times newspaper, Mr Reznikov praised the UK for being “key” in the transition from providing Ukraine with Soviet-era weapons to Nato-standard air defence systems and ammunition.
He said weapons deliveries needed to be sped up.
“We need more, quickly, to save the lives of our soldiers. Each day we’re waiting for howitzers, we can lose a hundred soldiers,” he said.
“We have approximately 700,000 in the armed forces and when you add the national guard, police, border guard, we are around a million strong,” the defence minister said.
However, Dr Jack Watling, senior research fellow at the Royal United Services Institute, cautioned against the figure.
“It’s not a million strong force that will be conducting a counter-attack,” Mr Watling told the BBC.
“Normally you would want operational surprise when you launch a counter-attack, so announcing it publicly is partly about forcing the Russians to have to commit resources more widely to guard against this threat.”
Much of the focus of this war has been on the Russian offensive in the industrial east – the area known as the Donbas – but it is access to the coast that many consider to be more important to Ukraine in the long term.
Counter-offensives there have been limited so far – retaking small sections of territory.
But Ukraine is making ever louder noises about recapturing occupied Kherson and Zaporizhzhia.
Overnight their southern military command announced strikes had destroyed two Russian command posts – that followed a call from the deputy prime minister for people to leave the areas – ahead of what Iryna Vereshchuk said would be “a huge battle”.
UK Prime Minister Boris Johnson announced a new UK-led training programme in June for Ukrainian forces that has the potential to train up to 10,000 troops every 120 days.