“There’s always a ‘no’ first: No tanks. No missiles. No fighter jets,” he told Al Jazeera, referring to multiple times that Western allies have either refused to provide certain types of weapons to Ukraine or have strictly regulated their use. Denys withheld his last name and the location of his military unit in accordance with wartime regulations.

“And each ‘no’ costs lives. Not just ours. We’re big boys, we’ve seen life a bit, but those of children, the little children burned alive or blown to pieces …” the 27-year-old said, close to yelling, as he stood between a blossoming linden tree and an ice-cream kiosk in central Kyiv. “And then there’s a ‘maybe, maybe,’ and it goes on for months, and then there’s a ‘yes,’ but it’s always too late.”

Eventually, Western nations did agree to supply tanks, missiles and fighter jets – but after agonisingly long deliberations that cost lives, he said.

The latest “yes” from the United States and nearly a dozen Western nations that follows Russia’s recent advance and the relentless bombing of Kharkiv, Ukraine’s second-largest city, grants their permission to use the advanced weaponry they have supplied – or will supply soon – to strike inside Russia.

Washington and its allies have been afraid of antagonising Russia, whose President Vladimir Putin has repeatedly suggested that the use of nuclear weapons is on the table in the event that Ukraine or the West cross yet another “red line” such as the shelling of Crimea and Putin’s pet project, a bridge that links it to mainland Russia.

But Ukraine has already crossed many military and political Rubicons, including the expulsion of Russian troops from occupied areas and drone strikes on airfields, military bases, ports and oil depots deep in Russia. These acts have left Moscow fuming, but not enough to use nuclear weapons.

The latest Western “yes”, which came on Thursday and followed months of pleas from Kyiv, is more of a “yes, but”.

The White House said that Kyiv can start using US-supplied weapons for “limited strikes” within Russia – but only in areas adjacent to the northeastern Kharkiv region that sits along the Russian border.