BERLIN, June 2, 2025 (BSS/AFP) - Germany's president on Monday congratulated nationalist Karol Nawrocki on winning Poland's presidential election, calling on the two countries to "cooperate closely based on democracy and rule of law."

Poland and Germany are key to "ensure a future of security, freedom and prosperity for Europe", Frank-Walter Steinmeier said in a statement, after Nawrocki defeated pro-EU Warsaw Mayor Rafal Trzaskowski in a runoff Sunday.

The nationalist historian's victory is a major blow to Poland's pro-EU government and could revive tensions with the bloc as well as with Berlin.

After new Chancellor Friedrich Merz visited Warsaw last month, Nawrocki accused Poland's Prime Minister Donald Tusk of being the "butler" of the German state.

He has frequently called for Berlin to pay reparations for World War II, when Nazi Germany invaded Poland.

He told a Polish daily that "reparations are about historical justice" and pledged to "fight for them from the first day of my presidency".

In his statement, Steinmeier said that Berlin "is aware of its perpetual responsibility for the great suffering that Germans have brought upon Poland".

Migration is another issue set to cause friction, with Nawrocki urging stricter border controls with Germany to stop migrants from crossing into neighbouring Poland.

Soon after taking office, Merz announced plans to crack down on irregular migration by rejecting most asylum seekers at its borders -- moves that have already drawn criticism from Tusk.

Steinmeier nevertheless said he hoped that Poland and German would work closely together "in a very challenging time for Europe"

"A strong Europe needs good German-Polish cooperation," he said.