Wojciech Kolarski, an adviser to Polish President Andrzej Duda, said Trump would arrive on August 31 and stay in the country until September 2, public broadcaster Polish Radio’s IAR news agency reported.
Previous reports suggested Trump’s visit would be shorter.
A Polish newspaper reported earlier this month that Trump would spend two days in Poland when he visits for the WWII anniversary.
Polish Deputy Prime Minister Jacek Sasin was this month cited as saying that Trump would definitely be among foreign leaders taking part in international commemorations in the Polish capital on September 1.
Polish presidential spokesman Błażej Spychalski told public broadcaster Polish Radio’s IAR news agency at the time that Trump's visit would only be definitively confirmed when it is officially announced by the White House.
Spychalski, press spokesman for the Polish head of state, was earlier this year quoted as saying that officials from European Union, NATO and Eastern Partnership countries had been invited to take part in observances of the 80th anniversary of the outbreak of World War II on September 1.
International leaders including German President Frank-Walter Steinmeier and Chancellor Angela Merkel have since confirmed they will attend, according to media reports.
Spychalski said in March that no Russian officials had been invited to visit Poland to mark the anniversary.
Trump last month hosted Poland's Duda at the White House, a meeting during which the two presidents approved plans for a stepped-up American military presence in Poland.
Source: IAR, TVP Info, onet.pl