Six American troops were hospitalized – two with serious inuries– after the van they were riding veered off the road and rolled over Sunday in southwestern Poland. A seventh troop was treated at the scene.

Local police said Monday the crash happened near Trzebien, on the A18 road, as the troops were traveling toward Wroclaw on a routine mission.

Four of those hospitalized for later released and were recovering, while the two seriously injured troops remained hospitalized in stable condition, TSC Public Affairs Officer Maj. Selwyn Johnson told the Associated Press.

The Pentagon did not immediately return Fox News’ request for comment Monday morning.

POLISH PRESIDENT PROPOSES PERMANENT US BASE CALLED 'FORT TRUMP,' DESPITE NATO RESTRICTION

The troops are part of the 21st Theater Sustainment Command (TSC) based in the Zagan region. They are part of a strategy to shore up NATO member Poland’s defense capacity at a time of heightened Russian military activity.

Last year, Poland’s defense minister said his country would be open to having thousands of American troops permanently stationed as a possible deterrent to Russia.

Later President Andrzej Duba told President Trump that if the U.S. were to create a permanent base in Poland, his country would pay more than $2 billion for the project and call it “Fort Trump.”

Duda emphasized that his country was "willing to make a very major contribution to the United States to come in and have a presence in Poland."

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A 1997 NATO-Russia agreement technically forbids U.S. or NATO troops from being permanently based in former Warsaw Pact countries, including Poland.

Fox News' Lucas Tomlinson, Travis Fedschun and Gregg Re contributed to this report.