Sending US-made F-16 fighter jets to Ukraine would be a “serious problem” for Poland, which only has some 50 aircraft of this type, Poland’s President Andrzej Duda told the BBC on February 12.

His comments indicate that, despite their criticism of Western European members of Nato for being slow to send heavier and more sophisticated weaponry to Ukraine, the countries on Nato's eastern flank are also struggling to carry through with their own transfers of arms to Kyiv.

Duda was responding to Ukraine’s leader, President Volodymyr Zelenskyy, calling on his country’s Western European allies to send in more arms, including jets, during his Europe tour last week.

"I appeal to you and the world with the simple, and yet most important words – combat aircraft for Ukraine, wings for freedom,” Zelenskyy told the UK parliament.

Poland, one of Ukraine’s staunchest allies in the country’s war against Russian aggression, said, however, that sending jets is a highly complex thing to do.

"We have not enough… and we would need many more of them,” Duda told the BBC.

The Polish president also said that F-16s require complex maintenance and it was "not enough just to send a few planes”.

Slovakia, another strong supporter of Ukraine also admitted at at the weekend that sending its Soviet-made MiG-29 fighter jets to Ukraine would be complicated. Caretaker Prime Minister Eduard Heger told Slovak public broadcaster RTVS that he will consult constitutional lawyers over the planned transfer.  Heger has been in charge of a caretaker cabinet, which has curtailed powers, since the second half of December after losing a vote of no confidence.

“It is necessary to examine whether a caretaker cabinet is competent [to authorise the MiG-29 deliveries] or not,” Heger commented for RTVS. 

Slovakia has long offered to transfer MiG-29 fighter jets to Ukraine but only received an official request from Kyiv last week, Heger told the BBC on February 12. He said it could take weeks for the authorisation to go through the government and parliament.

Poland and Slovakia have been among the Western countries to have pushed for sending tanks to Ukraine, an effort, which eventually came through, with several European countries and the US all gearing up to send tanks and train Ukrainian troops to operate them.

With every supply of heavier weapons, however, the West and Nato are worried that the war could spill over Ukraine’s borders to engage individual countries or even the entire alliance in a war with Russia. 

That said, over a series of incremental steps, the West has indeed supplied Ukraine with a range of more and more sophisticated weaponry, including long-range missile systems, with which Ukraine is able to strike deep behind enemy lines.