Donald Tusk made the statement at a media briefing in Kyiv on Monday.
Speaking to reporters alongside Ukraine's President Volodymyr Zelensky, after their talks earlier in the day, the Polish prime minister said that Warsaw and Kyiv would "continue military cooperation."
He stated that Poland would "unwaveringly support" Ukraine's defence against the Russian invasion.
Tusk added that the "Polish and Ukrainian governments will support the development of arms-making companies."
He said it was important to "quickly boost the defence capabilities of Poland and Ukraine."
Poland's prime minister said he and Zelensky had agreed "ways to finance Poland's assistance to Ukraine," adding that "Poland will be ready to produce and support Ukraine with military hardware."
Tusk said some of Polish arms deliveries could be carried out "on a commercial basis," as a way of ensuring Poland and Ukraine's "national security as well as shared interests."
Poland's prime minister also said that Ukraine's president, as well as the country's Cabinet under Denys Shmyhal, on Monday "reaffirmed their willingness to work together to resolve Poland-Ukraine issues such as grain imports and the border blockade by transport companies."
Tusk stressed that Warsaw and Kyiv would "seek practical solutions in friendly talks and maybe there won't be a need to consult international institutions," Polish Radio's polskieradio24.pl reported.
Poland's prime minister stated that "the fate of the free world is being decided in Ukraine," and that he could not choose any other country for his first foreign visit outside the European Union, after taking office last month.
Monday is day 698 of Russia’s war on Ukraine.
Russia invaded Ukraine on February 24, 2022, launching the largest military campaign in Europe since World War II.
Source: IAR, polskieradio24.pl, Interia.pl