Ukraine is pushing its Western allies to provide it with fighter jets, a week after winning pledges of sophisticated modern tanks to help it beat back Russia’s invasion force after almost a year of fighting.

Ukrainian Defense Minister Oleksii Reznikov was due in Paris on Tuesday where discussions about the possible delivery of fighter jets to Ukraine was expected to be on the agenda.

After months of haggling, Ukrainian authorities last week persuaded Western allies to send the tanks. That decision came despite the hesitation and caution of some NATO members, including the United States and Germany.

There was no indication that a decision on warplanes to Ukraine might come any time soon and no sign that Western countries have changed their earlier stance on the issue. Some Western leaders have expressed concern that the move could escalate the nearly year-long conflict and draw them deeper into the war.

The U.K. government, which has been one of Kyiv’s staunchest diplomatic supporters and military suppliers, said that sending its fighter jets is “not practical.”

Prime Minister Rishi Sunak’s spokesman, Max Blain, said “the U.K.’s Typhoon and F-35 fighter jets are extremely sophisticated and take months to learn how to fly.”

“Given that, we believe it is not practical to send those jets into Ukraine,” he said Tuesday, though he didn’t say that the U.K. was opposed to other countries sending planes.

Asked by a reporter Monday if his administration was considering sending Ukraine F-16 fighter jets to Ukraine, U.S. President Joe Biden responded “no.”

Kyiv officials have repeatedly urged allies to send jets, saying they are essential to challenge Russia’s air superiority and to ensure the success of future counteroffensives that could be spearheaded by tanks recently promised by Western countries.

Ukraine’s allies also have ruled out providing Kyiv with long-range missiles able to hit Russian territory, signaling a similarly cautious stance on warplanes.

Asked Tuesday about the supplies of Western weapons to Ukraine, Russian Foreign Minister Sergey Lavrov repeated the Kremlin’s view that “NATO long has been directly involved into a hybrid war against Russia.”

He added after the talks in Moscow with Egyptian Foreign Minister Sameh Shoukry that the Russian military will “take all the necessary measures to derail the fulfillment of Western plans.”

He said that Shoukry conveyed a message from U.S. Secretary of State Antony Blinken about Ukraine, which repeated the previous calls from Washington for Russia to withdraw.

Lavrov said “Russia is ready to hear any serious — I want to underline this word — proposal aimed at comprehensive settlement of the current situation.”

Both Ukraine and Russia are believed to be building up their arsenals for an expected offensive in coming months. The war has been largely deadlocked on the battlefield during the winter.

As in previous debates about how to help Ukraine, Poland is a leading advocate in the European Union for providing military aid. Poland, Slovakia and the Baltic countries on NATO’s eastern flank feel especially threatened by Russia.

Asked about Lithuania’s call for fighter jets and long-range missiles for Ukraine, Kremlin spokesman Dmitry Peskov said the comments “reflected an aggressive approach taken by the Baltic nations and Poland, who are ready to do everything to provoke further escalation without thinking about consequences.”

“It’s very sad that the leaders of big European countries that drive the European agenda don’t fulfill a balancing role to offset such extremist inclinations,” Peskov said in a conference call with reporters.

French President Emmanuel Macron said Monday that France doesn’t exclude sending fighter jets to Ukraine, but he laid out multiple conditions before such a significant step is taken.

The conditions, he said, include not leading to an escalation of tensions or using the aircraft “to touch Russian soil,” and not resulting in weakening “the capacities of the French army.”

He also said Ukraine must also formally request the planes, something that could happen when Reznikov sits down for talks in Paris.

German Chancellor Olaf Scholz appeared to balk at the prospect of providing fighter jets, suggesting Sunday that the reason for the entire discussion might be down to “domestic political motives” in some countries.

Dutch Prime Minister Mark Rutte said Monday there are “no taboos” in efforts to help Ukraine. But he added that sending jets “would be a very big next step.”

NATO-member Croatia’s president, meanwhile, criticized Western nations for supplying Ukraine with heavy tanks and other weapons. President Zoran Milanovic argued that those arms deliveries will only prolong the war.

Earlier in the conflict, discussions focused on the possibility of providing Kyiv with Soviet-made MiG-29 fighter jets that Ukrainian pilots are familiar with. In March, the Pentagon rejected Poland’s proposal to transfer its MiG-29 fighter jets to Kyiv through a U.S. base in Germany, citing a high risk of triggering a Russia-NATO escalation.

Western warplanes would offer Ukraine a major boost, but countering Russia’s massive air force would still be a major challenge.

Ukraine inherited a significant fleet of Soviet-made warplanes, including Su-27 and MiG-29 fighter jets and Su-25 ground attack aircraft.

Switching to Western aircraft would require Ukrainian crews to undergo long training and would also raise logistical challenges linked to their maintenance and repair.

Russia methodically targeted Ukrainian air bases and air defense batteries in the opening stage of the conflict, but Ukraine has been smart about relocating its warplanes and concealing air defense assets, resulting in Russia’s failure to gain full control of the skies.

After suffering heavy losses early during the conflict, the Russian air force has avoided venturing deep into Ukraine’s airspace and mostly focused on close support missions along the frontline.

The Ukrainian air force faced similar challenges, trying to save its remaining warplanes from being hit by Russian fighter jets and air defense systems