WASHINGTON -- U.S. President Joe Biden said on Monday that he won't approve sending F-16 fighter jets to Ukraine.

"No," Biden said in response to a question about the possibility of such a decision.

As he spoke, Biden arrived back at the White House from a trip to Baltimore, Maryland. Biden also said he was planning to visit Poland but didn't yet know when.

The president's remarks came as debate picked up steam over whether to arm Ukraine, which has been in conflict with Russia for nearly a year, with Western-made fighter jets.

Asked about the administration's decision on potential delivery of F-16s to Ukraine, U.S. Deputy National Security Advisor Jonathan Finer said during an appearance on MSNBC last Thursday that "we have not ruled in or out any specific systems."

"We have tried to tailor our assistance to the phase of the fight that the Ukrainians are in. I don't have an announcement to make one way or the other," he added.

Albeit a constant request from the authorities in Kiev, fighter jets have long been regarded by the West as a taboo in terms of military assistance for Ukraine, for fear that such deliveries would lead to an uncontrollable escalation of the conflict.

Ukrainian Foreign Minister Dmytro Kuleba said on Twitter last Wednesday that securing the provision of Western-type fighter jets are among the "new tasks ahead" for Ukraine. On the same day, the United States and Germany announced their respective decisions to send combat tanks to Ukraine.

Ukraine's plea for fighter jets met with refusal from Germany, whose chancellor, Olaf Scholz, recently said combat aircraft is not an item on Berlin's list of weapons for Ukraine.

"The question of combat aircraft does not arise at all," Scholz said in an interview with Tagesspiegel published on Sunday. "I can only advise against entering into a constant competition to outbid each other when it comes to weapons systems."