Germany will send Leopard 2 tanks to Ukraine and allow other countries such as Poland to do the same to help Kyiv fight off Russia's invasion.
The United States, in the meanwhile, may supply Abrams tanks, two sources familiar with the matter told Reuters.
While there was no official confirmation from Berlin or Washington by late on Tuesday, officials in Kyiv swiftly hailed what they said was a potential game changer on the battlefield in a war that is now 11 months old.
"A few hundred tanks for our tank crews – the best tank crews in the world. This is what is going to become a real punching fist of democracy against the autocracy from the bog," Andriy Yermak, the head of Ukrainian President Volodymyr Zelenskyy's administration, wrote on Telegram.
Kyiv has pleaded for months for Western tanks that it says it desperately needs to give its forces the firepower and mobility to break through Russian defensive lines and recapture occupied territory in the east and south.
A German government spokesperson and the Foreign and the Defense Ministries in Berlin declined to comment.
The German decision concerns at least one company of Leopard 2 A6 tanks, said Der Spiegel magazine, which first reported the news. One company usually comprises 14 tanks.
"Today the Chancellor made a decision that no one took lightly. The fact that Germany will support Ukraine with the Leopard tank is a strong sign of solidarity," Christian Duerr, parliamentary leader of the co-governing Free Democrats (FDP), was quoted as saying by t-online news portal.
Frozen front lines
Front lines in the war, which stretch more than 1,000 kilometers (620 miles) through eastern and southern Ukraine, have been largely frozen in place for two months despite heavy losses on both sides. Russia and Ukraine are both widely believed to be planning new offensives.
Whether on not to supply Ukraine with significant numbers of heavy modern battle tanks has dominated discussions among Kyiv's Western allies in recent days.
Berlin has been pivotal, because the German-made Leopards, fielded by armies across Europe, are widely seen as the best option – available in large numbers and easy to deploy and maintain.
German Chancellor Olaf Scholz's Social Democrats have been wary of moves that could spur Russia to escalate the war, and what they regard as a risk of the NATO alliance being drawn into the conflict.
Russian President Vladimir Putin casts the "special military operation" that began when his troops invaded Ukraine on Feb. 24 last year as a defensive and existential battle against an aggressive and arrogant West.
Ukraine and the West call Russia's actions an unprovoked land grab to subdue a fellow former Soviet republic that Moscow regards as an artificial state.
Earlier Tuesday, Poland upped the pressure on Scholz to make a decision, saying it had formally sent a request to the German government to allow it to send some of its Leopards. Defense procurement rules mean Berlin must approve re-exports of the NATO workhorse tank by its allies.