French President Emmanuel Macron has called Polish PM Mateusz Morawiecki "a far-right anti-Semite who bans LGBT people", after being criticised for his talks with Russia's Vladimir Putin.
Mr Morawiecki compared Mr Macron's efforts to negotiating with Hitler.
The French president has held regular conversations with Mr Putin since the beginning of the conflict in Ukraine.
On Friday, Poland summoned the French ambassador over Mr Macron's comments, made to a French newspaper.
"How many times have you negotiated with Putin and what have you achieved?" Mr Morawiecki said on Monday.
"It's my duty to speak with him, we need it. I won't stop doing it, that's what allows us to take part in the negotiation," he said.
"By talking to him and to [Ukraine's] President Zelensky, we can help in the negotiation. At some point, there will be a ceasefire and peace will have to be built. It cannot be done without a guarantor, France is committed to be one of these guarantors."
It is not clear why Mr Macron accused Mr Morawiecki of anti-Semitism, although the Polish government has faced international criticism for laws making it harder for Jewish people to recover property lost during and after World War Two, as well as one making it an offence to link the Polish nation to Nazi crimes.
Mr Macron also said Mr Morawiecki wanted to help his rival Marine Le Pen in the French presidential election on Sunday.
Opinion polls show that Ms Le Pen has closed the gap on Mr Macron, who joined the campaign late and has seen his lead erode as Ms Le Pen focussed on a cost-of-living message.
He enjoyed a boost from his diplomatic efforts in the Ukraine conflict but that has faded, and he has tried to portray Ms Le Pen as someone sympathetic to Mr Putin.
A Polish government spokesman, Piotr Müller, rejected Mr Macron's accusation of anti-Semitism, saying he had gone "too far" with his choice of words.