President Donald Trump has announced he will be moving troops to Poland from Germany, more than halving the number of soldiers hosted by Berlin.
Mr Trump made the announcement on Wednesday after a visit by Polish leader Andrzej Duda at the White House.
It comes just four days before the Polish elections, which will see Mr Duda facing a close fight to retain the leadership.
"We are going to be reducing our forces in Germany" from 52,000 to 25,000 troops, Mr Trump said after an Oval Office meeting with Mr Duda.
"Some will be coming home and some will be going to other places. Poland would be one of those other places."
Mr Duda called it a "very reasonable decision" and said he had asked Mr Trump not to withdraw US troops from Europe "because the security of Europe is very important to me".
Mr Trump said that the move would send "a very strong signal" to Russia.
Voters in Poland will decide on Sunday whether to give Mr Duda a second term, and the timing of the meeting was criticised by his opponents as an attempt at a pre-election boost.
The meeting was Mr Trump's first with a foreign leader since the Covid-19 pandemic, which has killed more than 123,000 people in the US, hit in March.
"President Duda is doing very well in Poland," Mr Trump said after the third Oval Office meeting between the two men. "He's doing a terrific job."
On the timing of the meeting, he said: "The people of Poland think the world of him. I don't think he needs my help."
Last year, before British Prime Minister Boris Johnson was elected, Mr Trump called him the "exact right guy for the times" and said he would do "an excellent job".
Mr Trump has not said how many US troops would be shifted from Germany to Poland.
He also repeated his frequent accusation that Germany was not paying its fair share of Nato's defence budget.
Polish newspaper Dziennik Gazeta Prawna, reported that 30 F-16 fighter jets stationed in Germany could be moved to Poland with 2,000 troops.
Nato promised Russia in 1997 not to set up permanent bases in the former eastern bloc.
But as tension has grown, the alliance has rotated troops through front-line countries.
Even though the US troops would be rotated anyway, Polish officials have raised the prospect of a more permanent US presence.
German Defence Minister Annegret Kramp-Karrenbauer alluded to the agreement with Russia on Wednesday.
"If for example US troops in Europe are moved to Poland, this must be done with the Nato-Russia pact in mind," Ms Kramp-Karrenbauer told the Atlantic Council.
"We must not lose sight of this point."
The right-wing Mr Duda, who is backed by the governing Law and Justice party, is the frontrunner in Poland's election, but the centrist Europhile opposition candidate Rafal Trzaskowski has been catching up in polls.
US Representative Marcy Kaptur, a Democrat from Ohio who co-chairs the congressional Poland caucus, condemned the decision to host Mr Duda at this time.
"As a Polish-American and someone who deeply values the US-Poland relationship, I am troubled by President Trump's inappropriate efforts to insert himself into Polish domestic politics and boost President Duda's re-election with a White House visit," Ms Kaptur said.
"Unfortunately, President Trump's invitation is not surprising given his favorability toward strongmen and those who undermine democratic institutions."
This was the 11th meeting between the two presidents and Poland has raised the idea of naming a military base Fort Trump.