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."
Opening a Cabinet meeting on Tuesday, the Polish prime minister read out a message from a Polish Afghanistan veteran urging the government to defend Polish soldiers who served there.
"I got a medal from the Americans for treating them ... We were there for them with all our hearts," the text said.
Tusk told ministers: "I would like these words to reach our allies, so that no one ever again belittles the effort of our soldiers."
He called it "especially wrong" to dismiss a commitment that had cost some Polish soldiers their lives, and said that without mutual respect it was hard to imagine a readiness to sacrifice.
He added that he had hoped President Karol Nawrocki would also speak out.
"But I think I miscalculated," he said.
Włodzimierz Czarzasty, Speaker of the Sejm, Poland's lower house of parliament, called Hegseth’s remarks "another scandalous statement" from the US administration.
He noted that 44 Poles had died in Afghanistan and urged US officials "not to say things that hurt soldiers’ families and Polish national pride."
Foreign Minister Radosław Sikorski has also criticised the comments, while the head of the prime minister’s office, Jan Grabiec, said the families of Polish soldiers were owed an apology.
Allies mocked again
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 a little back, a little off the front line."
After criticism from European leaders, including the UK prime minister at the time, he praised the courage of British troops.
Amid the backlash, the US ambassador to Poland, Tom Rose, in January sought to ease tensions, saying on social media that Trump holds "deep respect for Poland’s sacrifice and its unwavering commitment to the NATO Alliance," including the service of Polish soldiers in Iraq and Afghanistan.
Rose said that Poland’s decision to fight alongside US forces was "no symbolic gesture," describing Polish participation as "meaningful, operational, and decisive."
He praised the "professionalism, courage and sacrifice" of Polish forces, adding that "the loyalty" and "solidarity" shown by Poland and its people was something "the American people will never forget."
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, IAR