The prime minister told Polish state-run radio on Tuesday that his own plan for EU voting reform, which would give the Polish vote more weight than the plan endorsed by Germany, is based on the population that the country would have today had not over six million Poles been killed in the six years of World War Two.
The remarks were confirmed by the broadcaster on Thursday.
"We're only demanding that which was taken from us," Kaczynski said afterwards in an interview. "If Poland had not experienced the years between 1939 and 1945, it would today be a country of 66 million if you look at the demographic data."
During World War Two, which began when Nazi Germany invaded Poland in September 1939, around 6.5 million Poles died, including three million Polish Jews. That was about one-fourth of the pre-war population.
Today, Poland's population is just under 38 million.
The comments are likely to do little to soothe ruffled feathers on both sides of the German-Poland border. The Poles have stuck to their threat to veto a watered-down EU treaty at a European Union summit opening Thursday unless they were given more voting powers.
The Polish prime minister said in a German newspaper Wednesday that his country would be committing "suicide" if it agreed to the German proposals on the voting system.
"They are trying to isolate and ignore Poland. We cannot agree to that. That would be suicide," he told the mass-circulation Bild.
Poland, the biggest of the ex-communist states that joined the EU in 2004, opposes the planned "double majority" system for making decisions affecting the entire bloc.
The Polish demands have been opposed by 25 EU states, with only the Czech Republic voicing support.
German Chancellor Angela Merkel on Thursday urged her fellow European Union leaders to work together for a "fair agreement" on a treaty to reform the EU's creaking institutions.
Ahead of a key European summit opening later in the day, where her EU presidency's plans for a reform treaty will be put to the test, Merkel said everyone "can contribute their ideas" but that an agreement was necessary.
"I hope we can all work together in the right spirit to come to a fair agreement because the European Union needs to be capable of acting in order to solve the many problems in the world with collective solutions," she said at a meeting of conservative leaders near Brussels.
European Commission President Jose Manuel Barroso, at the same gathering, stressed the need for reform so the EU's institutions can adjust to its growing size.
"We need to reinforce the capacity of the European Union to act," he said. "With 27 you cannot have the same rules as with 12."
Luxembourg Prime Minister Jean-Claude Juncker, the EU's longest-serving leader still in office, put the chances of a summit agreement at "50-50" and warned that no further EU enlargement would be possible without a new treaty.
Dutch Prime Minister Jan Peter Balkenende joined the chorus seeking a deal, despite holding out for more power for national parliaments.
"We need to reach consensus, because if you do not have success now, is there a guarantee that you will get it after six months?" he asked.
In addition to the Polish question mark, British objections to parts of Merkel's plans could yet scupper an accord. Britain has warned that it would prefer no agreement to a bad deal, while Polish leaders have said their country is even "willing to die" to defend its corner.