Duda highlighted close US-Polish defence ties through history and referred to "a very heated time indeed" in US politics in recent days but said relations could weather "any storms".

"We are ratifying this agreement today and throughout this process we are also waiting for the newly elected US president to take his oath and office," he said at the ceremony.

Duda, who is backed by the ruling populist right-wing Law and Justice (PiS) party, has come under fire from government opponents for his half-hearted response Saturday to Biden's victory.

"Congratulations to Joe Biden for a successful presidential campaign. As we await the nomination by the Electoral College, Poland is determined to upkeep high-level and high-quality PL-US strategic partnership for an even stronger alliance," he wrote.

Duda has cultivated a strong personal relationship with Trump and visited him at the White House in June -- the first foreign leader to do so since White House coronavirus lockdown restrictions were eased.

During the visit, which came just days before Duda's re-election, Trump hailed the Polish leader saying he was doing "a terrific job".