A fresh push by Britain and the Netherlands to provide Ukraine with F-16 fighter planes has exposed the latest fault line among Western allies who have wrangled repeatedly over sending powerful weapons of war, once again pitting a reluctant United States against some of its closest European partners.
Several European allies are prepared to give their F-16s to Ukraine. But the Biden administration, which must approve any transfers of the American-made planes, remains unconvinced that Ukraine needs the expensive jets, which are a staple of many modern military arsenals.
So deep is Washington’s skepticism that Kyiv’s pilots are currently not even allowed to train on the F-16s that are owned by European states, according to a senior Ukrainian official who spoke on condition of anonymity to frankly discuss the sensitive diplomatic issue.
American reluctance to allow training would severely limit a proposed new European coalition to help Ukraine obtain and fly F-16s — whether in the current conflict or to protect against any future aggressions by Moscow after the West turns its focus from the 15-month war.
“What’s really important here is to signal to Russia that we as nations have no philosophical or principled objection to supplying Ukraine capabilities that it needs, depending on what is going on in the battlefield,” the British defense minister, Ben Wallace, said on Wednesday in Berlin. He added: “This is up to the White House to decide whether it wants to release that technology.”
In Washington, a senior U.S. official said the Biden administration was still reluctant to send Ukraine its own F-16s, in part because the plane’s multimillion-dollar price tag would absorb too much of an already-dwindling pot of war funding. Instead, the U.S. official said, the administration is more concerned with speeding other American weapons to Ukraine in time for a counteroffensive against Russia, and that in any case the jets would not reach the battlefield for months at least — presumably, long after that battle had begun.
The U.S. official also spoke on condition of anonymity, as did four other senior Western officials in Washington and Europe who were interviewed for this story.
This would not be the first time the Biden administration had resisted allied demands to send more powerful and sophisticated weaponry to Ukraine. In each case it eventually reversed itself, allowing the transfer of powerful HIMARS missile launchers, Abrams tanks and Patriot air defense missiles.
And the U.S. official did not rule out the possibility of the Biden administration issuing re-export licenses to European militaries, enabling them to transfer their F-16s to Ukraine. Later Tuesday, after Britain and the Netherlands announced their so-called “fighter coalition,” Secretary of State Antony J. Blinken and the Dutch foreign minister, Wopke Hoekstra, spoke by phone to discuss Ukraine and other issues.
Mr. Hoekstra said on Wednesday that “we haven’t reached a solution yet” in what another senior European diplomat described as a slow-moving and difficult discussion.
“When we are ready to cross that bridge and are ready to communicate this, we will,” Mr. Hoekstra said.
The Netherlands is one of four European countries that the senior Ukrainian official said have quietly signaled they are ready to send F-16s to Kyiv. Its fleet, along with those of Denmark and Belgium, could provide at least 125 combat-ready F-16s, according to the International Institute for Strategic Studies, a British think tank that assesses military stockpiles globally. Norway, which retired its unspecified number of F-16s last year in a switch to the more advanced F-35 Joint Strike Fighter, is also ready to contribute, the Ukrainian official said.
Kyiv is asking — for now, at least — for only between 24 and 36, the official said.
Earlier this week, the British prime minister, Rishi Sunak, said the United Kingdom would begin training Ukrainian pilots, starting this summer, as part of a plan “with other countries on providing F-16 jets.” His announcement, wrapped in a new package of military aid, came during a visit to London by President Volodymyr Zelensky of Ukraine.
Without explicit American approvals, however, the training is likely to be limited to what the senior Ukrainian official described as merely technical language and tactical lessons that pilots would be taught, without ever touching an F-16.
With its powerful radar that can spot targets from hundreds of miles away and modern missiles, the F-16 contains classified and other highly restricted systems that the United States does not want duplicated or falling into hostile hands. It is among classes of weapons for which even allies must gain “releasability” permission from the Pentagon just to discuss the technology with outside partners, like Ukraine, a senior Defense Department official said.
Last month, Poland and Slovakia said they had sent Ukraine more than 20 Soviet-era MiG-29 fighter jets in advance of the counteroffensive. But Ukraine’s leaders have said the F-16 is better equipped to protect against airstrikes and to evade Russia’s own warplanes.
The Biden administration has frequently resisted sending more powerful weapons to Ukraine for fear of Moscow’s escalating its attacks. The concern has quieted of late because it is no longer clear, short of nuclear weapons, how Russia could escalate any more than it has.
“Giving Ukraine F-16s will deter Russia rather than ‘provoke’ it,” Ukraine’s foreign minister, Dmytro Kuleba, urged last month. “Time to take this step.”
Douglas Barrie, an I.I.S.S. military expert, said it would be surprising if the Biden administration had not given “at least some kind of tacit nod and a wink” of approval for the European plan to help procure F-16s for Ukraine, and train its pilots, before moving ahead.
He said the fighter jets could play a key role in defending Ukraine, including “to continue to deny the Russians the kind of the air superiority they have failed to establish.” Whether the F-16s might be used to attack Russian positions will depend on what kinds of specific weapons package that Western allies agree to equip them with.
Experienced Ukrainian fighter pilots who are already skilled on Soviet-era jets could be trained to fly F-16s in “months rather than weeks, but not that many months potentially,” Mr. Barrie said. But he cautioned that any intensive training in the near future could pull pilots away from the war at a time when Ukraine needs as much of its air force as possible ready to fly.
“You don’t want to kind of have a drop-off in capability, obviously, in the middle of a war,” Mr. Barrie said.
But Ukrainian officials say they are more worried about a different kind of diversion — that of Western support as war fatigue sets in and funding dries up. They are concerned particularly with the United States, where some Republicans, including candidates in next year’s presidential election, are already questioning how much more support the country should give.
That may also be on the minds of a group of 14 Democrats and Republicans in Congress who on Wednesday urged President Biden to unlock the F-16s without delay.
“As we saw with the initial hesitancy by our allies to provide tanks to Ukraine, U.S. leadership is crucial for providing Kyiv with additional resources and new capabilities,” the lawmakers wrote in a letter to the White House that was coordinated by Representative Jared Golden, a Maine Democrat.
“The provision of F-16 fighter aircraft to Ukraine is essential to effectively end this war on just terms,” they wrote.
Steven Erlanger contributed reporting from Brussels, and Christopher F. Schuetze from Berlin.
