Speaking to cadets at the University of Tennessee in Knoxville on Saturday, Hegseth recalled his own service in Afghanistan.
He said that few allied countries had really contributed to the mission, "maybe five," or "actually closer to one or two."
The Pentagon chief added that troops had joked that the name of the international force, ISAF, stood for "I Saw Americans Fighting."
In a post on X on Sunday, Polish Deputy Prime Minister and Foreign Minister Radosław Sikorski said Hegseth should repeat his remarks to the families of the 44 Polish soldiers who died securing Ghazni, a province he described as "tough."
Jan Grabiec, head of the Polish prime minister’s office, said allies should not mock blood they had shed together.
This is not the first time Hegseth has mocked allies' role in Afghanistan.
He made a similar joke about ISAF last year, which also drew criticism.
President Donald Trump later said America’s allies in Afghanistan had "stayed little back, a little off the front line."
After criticism from European leaders, including the UK prime minister, he praised the courage of British troops.
The NATO mission in Afghanistan was the only time the alliance has invoked Article 5, its mutual defence clause.
More than 1,000 NATO soldiers were killed, including 459 British and 44 Polish personnel.
Poland, which backed the US-led operation from 2001, kept troops in Afghanistan for almost 20 years, until 2021.
More than 33,000 Polish soldiers and defence ministry staff served there.
From 2007, Poland was responsible for two Afghan provinces, and its contingent peaked at more than 2,500.
Forty-three Polish soldiers and one civilian paramedic died, and more than 200 people were wounded.
(ał/gs)
Source: PAP