John Kirby, the spokesman for America's National Security Council, made the statement at a press briefing on Wednesday, public broadcaster Polish Radio's IAR news agency reported.
Poland's new Cabinet, led by Tusk, was sworn into office by President Andrzej Duda earlier in the day, ending eight years of rule by the conservative Law and Justice (PiS) party.
Asked by Polish Radio's Washington correspondent how this would impact the US-Poland relationship, Kirby said that "Poland's a key NATO ally" and that Washington has "a great relationship" with Warsaw.
Poland is 'an extraordinary supporter of Ukraine'
He described Poland as "an extraordinary supporter of Ukraine, and of our efforts to help Ukraine."
Referring to the change of government in Poland, Kirby said: "We have every expectation that the closeness of our relationship and strong alliance and bond between us and Poland will continue."
The US official declined to say whether US President Joe Biden would invite the new Polish prime minister to the White House, the IAR news agency reported.
Polish PM, NATO chief discuss 'continued support for Ukraine'
Meanwhile, NATO Secretary-General Jens Stoltenberg on Wednesday held a phone call with Tusk to congratulate him on his reappointment as Poland's head of government.
Stoltenberg wrote on the X social media platform that he looked forward to working with Tusk again, and described the Polish prime minister as an "old friend and colleague."
The NATO chief said the two had also discussed "the importance of ensuring continued support for Ukraine."
Paris 'delighted to work' with Tusk on 'strengthening French-Polish relations'
France's foreign ministry has also issued congratulations, saying in a statement that Paris would be "delighted to work" with Tusk and the new Polish Cabinet on "strengthening French-Polish relations in every area."
The French foreign ministry added that France and Poland "remain determined to continue our support for Ukraine in the long term."
The Quai d’Orsay said France and Poland were "bound by their longstanding friendship" and committed to moving the EU forward in such priority areas as the energy transition, the rule of law, defense and migration."
Thursday is day 659 of Russia's war on Ukraine.
Russia invaded Ukraine on February 24, 2022, launching the largest military campaign in Europe since World War II.
(pm/gs)
Source: IAR, French Ministry of Foreign Affairs