An anti-missile system Germany offered to send to Poland should instead go to Ukraine, Warsaw said, raising concerns that such a move would signify an escalation of NATO involvement in the war in eastern Europe.
Others believe the Polish government's rebuff was a mistake.
Poland's surprising response to Berlin's offer was welcomed by Kyiv, desperate to protect its airspace as continued barrages of Russian missiles have knocked out power across the country.
But Germany's Defence Minister Christine Lambrecht stressed that the use of NATO defence systems outside its territory needs to be agreed upon by all member states.
"It is important to us that Poland can rely on allies to stand by each other, even in difficult times, and especially Poland in its exposed position," Lambrecht told reporters in Berlin.
"That's why we have offered to support air policing and Patriots, but these Patriots are part of an integrated air defence of NATO, that is, they are intended for NATO territory," the minister said.
"If they are used outside the NATO area, then it has to be agreed with NATO and with the allies beforehand."
In Poland, critics of the populist ruling party, PiS, accused it of sacrificing the country's security with a war next door in Ukraine for the sake of a domestic political struggle which exploits anti-German sentiment for short-term gain.
The Rzeczpospolita daily newspaper called the new proposal by Poland's leaders "shocking," arguing that it would require sending German soldiers operating the system to Ukraine.
"That, in turn, would involve NATO in a direct clash with Russia, something the alliance has been trying to avoid from the beginning," deputy editor Michal Szuldrzynski wrote.
"This proposal affects Poland's credibility
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