The unity of Ukraine's Western allies was under strain over the possibility of providing Kyiv with fighter jets to help beat back Russia's invasion, amid fears of escalating the nearly yearlong conflict.

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

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.

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

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 Reznikov sits down for talks in Paris.

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.

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."

Biden's deputy national security adviser, Jon Finer, said in an MSNBC interview last week that the U.S. would discuss fighter jets "very carefully" with Ukraine and allies.

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."

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.