WASHINGTON - The Pentagon, in a significant shift, said Tuesday that it will send M1 Abrams tanks to Ukraine by the fall, after facing scrutiny for initially saying it could take a year or two to procure the powerful weapons and get them to the battlefield.

The new plan calls for refurbishing tank hulls already in the U.S. arsenal, officials said. President Joe Biden, under intensifying pressure from Ukrainian officials, agreed in January to pledge 31 M1 tanks as part of a long-term arrangement that afforded German leaders political cover so that they could approve the immediate provision of Leopard battle tanks.

Brig. Gen. Patrick Ryder, a Pentagon spokesman, said that when the United States promised to provide Ukraine with the Abrams, the intent was to provide its more advanced variant, the M1A2. But, he said, officials continued "exploring options to deliver the armored capability as quickly as possible" and settled on refurbishing older M1A1 variants, allowing for expedited delivery. He did not clarify where it found those hulls in the American arsenal.

"This is about getting this important combat capability into the hands of the Ukrainians sooner rather than later," Ryder told reporters during a news conference.

Both versions of the tank have a 120mm cannon and machine guns, while the M1A2 typically also includes digital controls, improved sensors and a thermal viewer for the tank's commander.

Ryder declined to specify on Tuesday where the refurbishment will occur, but officials familiar with the work have said they anticipate it will take place at a government-owned facility in Lima, Ohio. General Dynamics Land Systems operates the plant, the only U.S. factory building tanks.

The Pentagon's disclosure came as Russian President Vladimir Putin and Chinese leader Xi Jinping hold talks in Moscow, where the two leaders promised to deepen ties. The closely watched meeting has fueled concern in the United States and Europe that Beijing will come to the Kremlin's aid as its military continues to suffer massive losses in Ukraine and its defense industry, hobbled by Western sanctions, struggles to replenish destroyed or expended weapons.

NATO's secretary general, Jens Stoltenberg, told reporters in Brussels on Tuesday that he had seen no proof China is delivering weapons to Russia but said there are signs that Russia has requested them and that Beijing is considering doing so.

In Washington, a bipartisan group of senators urged the Pentagon to conduct an "urgent and comprehensive" assessment of what it would need to counter Russia in Europe should conflict erupt between the nuclear powers. The lawmakers cited Russia's extensive combat losses, estimated to be approaching 200,000 dead and wounded, and the Defense Department's current plan to next assess its needs there in 2026.

"Put simply, the Ukrainian Armed Forces have significantly degraded Russia's conventional forces over the past year," their letter to Defense Secretary Lloyd Austin said. It was signed by Sens. Tom Cotton, R-Ark., Roger Wicker, R-Miss., Richard Blumenthal, D-Conn., and Angus King, I-Maine.

The senators added that Western sanctions have constrained Moscow's ability to rebuild its conventional forces and that Pentagon officials often cite assessments that could be outdated as justification for not providing Ukraine's military with certain additional capabilities.

"Russia's military is not the same as it was in 2021, and shows no signs of returning to its pre-invasion state in the near term," the senators wrote. "Our European warfighting requirements should reflect this new reality - not in 2026, but now."

The Pentagon did not immediately respond to questions about the senators' letter.

The administration's new timeline for transferring tanks to Ukraine follows public remarks by some officials who had indicated that a range of options was being evaluated. Army Secretary Christine Wormuth told reporters in February that all of the plans under consideration would take months to complete. One factor, she said, was that some allies already have deals to buy Abrams tanks from the United States.

"Some [options] could presumably get tanks to the Ukrainians more quickly but might, you know, disrupt relations with important allies and partners," Wormuth said. "So we're laying all that out."

The administration initially denied Ukraine’s plea for tanks while noting that the Abrams creates a massive logistical burden on the battlefield, instead supplying Bradley and Stryker fighting vehicles and suggesting it would make sense for the Germans to supply its smaller Leopard tank instead. In what has become a pattern while assessing Ukraine's battlefield needs, Biden eventually relented, assessing that the issue would not be resolved without an American commitment of tanks.

A similar conversation has percolated for months about providing Ukraine with fighter jets. Ukrainian officials have asked repeatedly for American-made F-16s, but the Biden administration has assessed that providing them now does not make sense, considering the training and maintenance they require and the significant threat posed by Russian surface-to-air missiles.

Last week, Poland and Slovakia, both NATO allies, announced that they would provide Ukraine with MiG-29 fighter jets. U.S. officials said that sending MiGs to Ukraine makes more sense because they already are familiar with the aircraft and that the answer on providing F-16s has not changed.