The leader of Germany's largest opposition party, Friedrich Merz, met Polish Prime Minister Mateusz Morawiecki on Thursday.
The visit comes amid frustration on Warsaw's part that Berlin is not providing sufficient backing to Ukraine.
Although the pace and breadth of arms deliveries have picked up in recent weeks, Berlin has not shaken the perception it is reluctant to supply heavy weapons to Kyiv, as it seeks to fight off the Russian invasion.
Morawiecki told the conservative German politician that while he saw economic relations as good between the two nations, Germany's arms deliveries to Ukraine or Poland were "not satisfactory," his spokesperson Piotr Mueller said.
During his visit to Warsaw, Merz also spoke with Donald Tusk of the opposition Civic Platform.
Their talks came a day after Merz met Jaroslaw Kaczynski, the head of Poland's ruling conservative nationalist Law and Justice (PiS) party, according to the Wiadomosci news site.
Kaczynski told Merz that Germany still owes Poland reparations for damage suffered during World War II, a question Berlin argues has been settled since reunification in 1990.
Merz tried to direct attention to joint projects, as relations shift between the two nations, as Poland provides extensive support to Ukraine.
International military aid is frequently channelled through Poland.
Merz conceded that some criticism was justified, citing Berlin's slowness on a three-way exchange in which Germany is to hand over tanks to Poland in exchange for its arms aid to Ukraine.
Relations between Poland and Germany are somewhat tense, in contrast to the easier relationship between former chancellor Angela Merkel and Tusk, a former prime minister.
Merz's visit to Poland was the first by a senior German politician since the war began, aside from President Frank-Walter Steinmeier. He was also quicker to travel to Kiev than German Chancellor Olaf Scholz.
