(Bloomberg) -- Poland may deliver Soviet-era fighter jets to Ukraine in the coming weeks, a move that would cross a threshold among NATO member states cautious about sending air power.

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“This might happen within the next four to six weeks,” Prime Minister Mateusz Morawiecki told reporters on Tuesday, responding to a query on whether Warsaw would make a decision to send MiG-29 jets. He didn’t elaborate on other details, including the size of a contingent.

Ukrainian President Volodymyr Zelenskiy and his military leadership have persistently demanded warplanes since the first days of the war as essential to driving back the Russian invasion. Those calls were renewed this year when western members of the transatlantic alliance abandoned a political taboo and pledged battle tanks to Kyiv, raising speculation that fighter jets would be the next barrier to fall.

The US and Germany have said sending air power isn’t on the agenda, with President Joe Biden specifying “for now.” The UK is assessing the longer-term possibility of sending planes.

But Poland has been among allies in the North Atlantic Treaty Organization most vocal about weapons deliveries to Ukraine. When Warsaw offered in the first weeks of the war to dispatch MiGs by way of a US airbase, the Pentagon said the arrangement was “not tenable.”

Polish President Andrzej Duda has said that his country doesn’t have the capacity to donate any of its 48 American-made F-16 jets, since such a move would require a joint decision from NATO members. But deliveries of Soviet-era hardware would be on the table.

Slovakia, Poland’s NATO neighbor to the south, has also raised the prospect of MiG deliveries, though a decision has been held up by political infighting ahead of an early election in September. Other NATO allies with MiG jets in their inventories include, Bulgaria, Croatia and Romania.

(Updates with prime minister quote in second, allied comments from second paragraph.)

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