CNN— The leaders of the United States and Germany each announced Wednesday they will send contingents of tanks to Ukraine, reversing their longstanding trepidation at providing Kyiv with offensive armored vehicles and unleashing powerful new tools in Ukraine’s efforts to retake territory seized by Russia.

The announcement by German Chancellor Olaf Scholz that he will send Leopard 2 tanks was coupled with an announcement from US President Joe Biden that he was providing 31 M1 Abrams tanks to Ukraine, reversing the administration’s longstanding resistance to requests from Kyiv for the highly sophisticated but maintenance-heavy vehicles.

The dual announcements made for a landmark moment that followed weeks of intense pressure on Berlin from some of its NATO allies. The decisions were the result of prolonged diplomacy between Germany, the United States and other European allies, and come as Ukrainian President Volodymyr Zelensky prepares for a new Russian offensive this spring.

Speaking from the White House, Biden said the tanks would “enhance Ukraine’s capacity to defend its territory and achieve its strategic objectives” in both the near and long terms.

And while he touted the ability of the tanks to help Ukraine “counter Russia’s evolving tactics and strategy on the battlefield,” Biden insisted they should not be viewed by Moscow as an “offensive threat.”

“This is not an offensive threat to Russia. There is no offensive threat to Russia if Russian troops return to Russia, where they belong,” he said.

Earlier, Scholz told lawmakers in Germany’s parliament the decision to send Leopard 2 tanks had come after consultations with western allies.

“It is right that we advanced bit by bit. That is the only principle that can work in such dangerous conditions,” he said.

The dispute over whether the Germans would send Leopards to support Ukraine threatened to show some of the first cracks in the united Western response to Russia’s invasion of Ukraine. But the announcement from Scholz and Biden show the US and its allies are still working in lockstep when it comes to supporting President Volodymyr Zelensky and his nation’s fight against the Russians.

NATO Secretary General Jens Stoltenberg told CNN’s Kate Bolduan on “At This Hour” that the German and US decisions were “important announcements” and that he “welcomed US leadership” in making them happen.

“It will significantly strengthen their combat capabilities,” Stoltenberg said of the effect the tanks will have on Ukraine’s military.

US to send 31 Abrams tanks

The US decision to provide Abrams tanks to Ukraine represents an abrupt about-face from its earlier stated position. While the Biden administration had never taken the possibility of shipping American tanks entirely off the table, US officials said publicly last week that it was not the right time to send the 70-ton M-1 Abrams tanks because they are costly and require a significant amount of training to operate.

The tanks, instead, were repeatedly floated as a long-term option – even as critics said it was the right time, as Ukraine braces for the possibility Russia will mobilize more troops and launch a new offensive. Zelensky has consistently asked Western allies for modern tanks as his country prepares braces for an expected major Russian counteroffensive in the spring.

Yet after an intensive bout of diplomacy with Germany, who had made clear it would only send its Leopard 2 tanks to Ukraine if the United States offered up the Abrams, Biden has given the sign-off on sending the vehicles. The 31 Abrams will form a complete Ukrainian tank battalion.

“Abrams tanks are the best in the world. This is a tremendous new capability that Ukraine will be getting to boost its long term defenses,” a senior administration official said, noting that the tanks will be procured through the Ukraine Security Assistance Initiative funding.

Biden spoke by phone Wednesday with Scholz, Italian Prime Minister Giorgia Meloni, French President Emmanuel Macron and British Prime Minister Rishi Sunak to discuss continued military support for Ukraine. US officials said maintaining unity among the western alliance was a critical consideration as Biden and his team came around on sending the Abrams tanks.

The Abrams tanks will take months to arrive, senior administration officials said, and will require extensive training for Ukrainian troops on how to operate and service them. The US must navigate complicated supply chains for the components required for the tanks.

The procurement process will take months, the officials said, though Germany’s Leopards will arrive in the nearer term. In the meantime, the US will begin a “comprehensive training program” for the Ukrainians on the Abrams, which will require significant maintenance once they are deployed. The training will occur outside Ukraine.

The US is also procuring eight M88 recovery vehicles, the second official said, which will help “keep the Abrams tanks up and running.”

Speaking ahead of the president’s announcement, senior US officials framed the decision as an investment in Ukraine’s “longer term capabilities,” an indication the administration sees the now 11-month-long war extending well into the future. Ukraine hopes the new tanks can help it retake territory seized by Russia, including in the Donbas. That could also include Crimea, the peninsula annexed by Russia in 2014.

“We’ve been talking about tanks internally and we certainly have been talking about tanks externally, with allies and partners, for quite some time, given what we expect will be the kinds of fighting, that will occur in weeks and months ahead,” an official said.

Still, officials acknowledged the challenges in providing Ukraine the Abrams tanks were still steep.

“There are technical aspects to the Abrams which makes it a little bit more challenging than some systems that that we have provided Ukraine in the past,” a senior official said. “It is the most capable tank in the world, but it’s also sophisticated.”

The months required to procure, build and ship the tanks will allow Ukrainian fighters time to learn how to use and maintain them, the official said.

Germans to send 14 tanks to Ukraine

The Germans’ goal is to assemble two tank battalions with Leopard 2 tanks for Ukraine, the government statement said. In a first step, Berlin will provide a company of 14 Leopard 2 A6 tanks from Bundeswehr stocks, with the training of the Ukrainian crews to begin quickly in Germany. In addition to training, the package will also include logistics, ammunition and maintenance of the systems.

The German defense minister said the Leopard tanks could be operational in Ukraine in about three months. Boris Pistorius, speaking to reporters Wednesday, said training would come first, then the tanks would be sent east.

The German army has 320 Leopard 2 tanks in its possession but does not reveal how many would be battle ready, a spokeswoman for the Ministry of Defense previously told CNN.

Germany will also allow other countries to export the battle tank, it said. Poland on Tuesday formally asked for approval from Germany to transfer some of its German-made Leopard 2 tanks to Ukraine.

Several European countries also own some Leopards, and Poland had led an effort to re-export those to Ukraine even if Germany was not on board.

Addressing the German parliament following the announcement, Scholz said he had spoken to Zelensky before coming to parliament.

During his speech, the German leader said Germany together with the US and UK had sent the most weapons systems to Ukraine and insisted that his country would be at the forefront of support for Ukraine.

Sending Leopard 2 tanks to Ukraine will provide Kyiv’s forces with a modern and powerful military vehicle ahead of a potential Russian spring offensive. It will also come as a blow to the Kremlin, which has seen a growing campaign to equip Ukrainian troops with high-tech fighting systems as Russia’s ground war nears the one-year mark.

Germany had initially resisted a growing drumbeat of Western pressure to ship some of the tanks to Ukraine, with new German Defense Minister Boris Pistorius repeatedly calling for more time and insisting that the move would come with pros and cons for Berlin.

Allies back Berlin’s move

The UK had set the precedent for providing Ukraine with main battle tanks last week after it pledged to send Kyiv 14 of its British Army Challenger 2 tanks. The agreement crossed what had previously appeared to be a red line for the US and its European allies.

Ukrainian officials have consistently pleaded with their Western allies to provide modern battle tanks – to be used not only to defend their present positions but also to take the fight to the enemy in the coming months. Ukrainians fear that a second Russian offensive may begin within two months.

Although Ukraine has stocks of Soviet-era tanks, modern Western tanks provide a greater level of speed and agility. In particular, the Leopard’s relatively low-maintenance demands compared to other models lead experts to believe the tanks could help Ukraine quickly on the battlefield.

British Prime Minister Rishi Sunak hailed Germany’s move as the “right decision” in the wake of Wednesday’s announcement.

“The right decision by NATO Allies and friends to send main battle tanks to Ukraine. Alongside Challenger 2s, they will strengthen Ukraine’s defensive firepower. Together, we are accelerating our efforts to ensure Ukraine wins this war and secures a lasting peace,” Sunak wrote on Twitter.

Ukrainian President Volodymyr Zelensky’s chief of staff welcomed the news and reiterated the country needed “a lot” of Leopard tanks. Writing on Telegram, Andriy Yermak said: “The first tank step has been taken. Next up is the ‘tank coalition’. We need a lot of Leopards.”

Polish Prime Minister Mateusz Morawiecki praised German Chancellor Scholz for his decision. “Thank you Olaf Scholz. The decision to send Leopards to Ukraine is a big step towards stopping Russia. Together we are stronger,” Morawiecki wrote on Twitter.

This story has been updated with additional developments.

CNN’s Natasha Bertrand, Oren Liebermann, Lauren Kent, Mick Krever and Rob Picheta contributed reporting.