Boris Johnson has piled pressure on western leaders to supply fighter jets to Ukraine.
The UK said it is not practical to provide sophisticated planes used by the RAF, such as Typhoons and F-35s, while US President Joe Biden has ruled out sending F-16 fighters.
But former prime minister Mr Johnson, who was in Washington for talks with senior politicians to bolster support for Ukraine, said its President Volodymyr Zelensky should be given all the equipment he needs.
Asked about the F-16 situation, he told Fox News: “All I will say is that every time we have said it will be a mistake to give such and such an item of weaponry, we end up doing it and it ends up being the right thing for Ukraine.
“I remember being told it was the wrong idea to give them the anti-tank shoulder-launched missiles. Actually, they were indispensable and the United States – under (former US president) Donald Trump – gave them the Javelins as well.
“They were indispensable in the battles to repel the Russian tanks.
“People said that we shouldn’t give the Himars (rocket launchers). I remember having arguments about the multiple-launch rocket systems, the MLRS.
“Actually, they have proved invaluable to the Ukrainians.
“We said the same about tanks.
“All I’m saying is save time, save money, save lives. Give the Ukrainians what they need as fast as possible.”
Mr Johnson rejected the idea Russian President Vladimir Putin could be prepared to turn the war into a nuclear conflict.
“He probably doesn’t even stop the Ukrainians if he did that – and we would put his economy into such a cryogenic paralysis that Russia wouldn’t come out of it for decades – so he’s not going to do that,” Mr Johnson said.
Downing Street said training Ukrainian pilots and ground crews on “extremely sophisticated” Typhoons and F-35s would take too long, though it does not oppose allies sending their own jets.
Mr Biden said on Monday he will not send warplanes to Kyiv.