The Republican delegation, led by Ryan McCarthy, a former US Secretary of the Army, met with the Polish president in the late afternoon, public broadcaster Polish Radio's IAR news agency reported.
It said the group included retired US Army generals James McConville and Edward Daly, both of whom held prominent military positions under Trump’s previous administration.
The Polish President’s Office did not immediately release photos or details of the meeting.
Following talks with Duda, the delegation met with Warsaw Mayor Rafał Trzaskowski at City Hall, according to the IAR news agency.
Trzaskowski, who also serves as deputy head of Poland’s main government party, the Civic Platform (PO), did not meet with reporters after the talks.
His office cited the sensitive nature of the discussions with the American delegation.
Trzaskowski later posted a photo on X, saying: "It is in Poland’s interest to persuade all those who influence the future US administration in Washington that continued support for Ukraine is essential for Europe’s stability and Poland’s security.”
He added: "Sec. McCarthy, Gen. McConville—thank you for a good meeting."
Earlier in the day, Polish Deputy Defence Minister Cezary Tomczyk told reporters that the visit by Trump's military aides underscored the United States' "forward-looking approach."
Tomczyk said the visit demonstrated "the Americans' strategic foresight" in meeting both the president and a potential future head of state.
If he wins a primary against Foreign Minister Radosław Sikorski, Trzaskowski will become a key contender to succeed Duda as president of Poland, according to recent surveys.
Tomczyk also said that the Trump associates' trip to Warsaw signalled the incoming US administration's "commitment to Poland as part of its strategic plans for the region."
He added that "key US Army generals" came to Warsaw "to gather insights from top Polish officials and bring them back to President Trump," Polish state news agency PAP reported.
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Source: IAR, PAP, TVP