The Leopards and armored fighting vehicles could be useful in reclaiming territory, since the grassy steppe in Ukraine’s south is suited “for tank or maneuver warfare,” said Jacob Funk Kirkegaard, a former Danish army intelligence officer who is now a senior fellow at the German Marshall Fund in Brussels.

Britain’s missiles and drones, he added, could be used to attack Russian bases in Crimea, the Black Sea peninsula that Moscow seized after a disputed referendum in 2014.

Russia’s Defense Ministry claims that the long-range missile, known as Storm Shadow, has already been fired by forces in eastern Ukraine, injuring six civilians on Saturday. The claim could not be independently verified, and there was no comment from Britain.

The Kremlin expressed anger at Britain’s pledge. “We take an extremely negative view of it,” said the Kremlin spokesman, Dmitri S. Peskov, according to the Russian state news agency TASS. But he added that the weapons would “not have any significant impact” on the war.

The United States has resisted sending long-range missiles to Ukraine, in part to avoid escalating the conflict with weapons that could reach into Russian territory. That is also one reason the Biden administration has not acceded to Ukraine’s requests for American-made F-16 fighter jets.