Invoking Churchill, Boris Johnson says the war is ‘Ukraine’s finest hour.’

LONDON — Prime Minister Boris Johnson of Britain told Ukrainian lawmakers on Tuesday that their heroic defense against Russia’s invasion would rank as “Ukraine’s finest hour,” invoking Winston Churchill’s famous declaration about Britons as they faced the Nazi onslaught at the beginning of World War II.

In the first address by a foreign leader to Ukraine’s Parliament, Mr. Johnson burnished his credentials as a stalwart supporter of Ukraine and a close ally of its president, Volodymyr Zelensky. In tone and themes, Mr. Johnson’s speech mirrored one that Mr. Zelensky gave to the British Parliament in March.

“You have exploded the myth of Putin’s invincibility and you have written one of the most glorious chapters in military history and in the life of your country,” Mr. Johnson said, referring to the Russian president, Vladimir V. Putin. “The so-called irresistible force of Putin’s war machine has broken on the immovable object of Ukrainian patriotism and love of country.”

“This is Ukraine’s finest hour, that will be remembered and recounted for generations to come,” he said in a video address recorded from Downing Street that was broadcast in the Parliament’s chamber.

Mr. Johnson insisted that no peace agreement with Russia should be foisted on the Ukrainians by outsiders. The courage of Ukraine’s citizens, he said, had earned the country the right to control its destiny. Moreover, he added, the West had been slow to grasp the threat posed by Mr. Putin when Russia seized Crimea in 2014.

“We collectively failed to impose the sanctions then that we should have put on Vladimir Putin,” he said. “We cannot make the same mistake again.”

Mr. Johnson announced that Britain would provide additional weapons to Ukraine, including electronic warfare gear, a counter-battery radar system and G.P.S.-jamming equipment. The package, valued at 300 million pounds ($375 million), comes on the heels of a $33 billion commitment of arms and humanitarian aid that President Biden has asked Congress to approve.

Britain recently announced plans to provide more sophisticated missiles and air-defense vehicles to the Ukrainian military, as well as armored vehicles to evacuate civilians from areas under attack. Mr. Johnson said Britain had also returned Melinda Simmons, its ambassador to Ukraine, to her post in Kyiv, the capital.

For Mr. Johnson, the invitation to speak to the Parliament, known as the Verkhovna Rada, was a significant gesture by Mr. Zelensky to a leader with whom he has forged a sturdy relationship over the course of dozens of phone calls. Last month, Mr. Johnson traveled to Ukraine and walked the streets of Kyiv with Mr. Zelensky, winning plaudits from Ukrainians, as well as people back home.

Mr. Johnson’s Conservative Party faces difficult local elections on Thursday, and he has yet to escape the shadow of a scandal over his attendance at social gatherings that violated Covid restrictions. But his firm stand on Ukraine has deflected some of the glare from his proliferating domestic woes.