Polish President Andrzej Duda said Monday a U.S. decision to allow Ukraine to use U.S.-made weapons to strike deep into Russia may be a decisive moment in the war.

Two U.S. officials and a source familiar with the decision revealed the significant reversal of Washington's policy in the Ukraine-Russia conflict Sunday.

"This decision was very necessary ... Russia sees that Ukraine enjoys strong support and that the West's position is unyielding and determined. It's a very important, potentially decisive moment in this war," Duda told journalists.

He also criticized Germany for saying it would not align its policy with the U.S., and expressed disapproval at German Chancellor Olaf Scholz's phone call with Russian President Vladimir Putin last Friday.

"Germany may be looking for opportunities, as the German press indicates, to reach some agreement with Russia in order to return to energy contracts and to be able to buy energy resources from Russia again," Duda said.

"Russia is brutally attacking Ukraine, and one of the leaders of the free world, one of the leaders of the West, a large European country, the strongest economy in Europe, is in talks with the aggressor. I absolutely believe that it was a mistake on the international political front."

Polish Prime Minister Donald Tusk had also criticized Scholz, saying that "no-one will stop Putin with phone calls."