NATO Secretary-General Mark Rutte said Wednesday that four U.S. soldiers who had been reported missing while training in Lithuania have now been found dead. He was unaware of any further details.

An official in the United States confirmed that four soldiers had been injured during a training accident. However, the official would not provide any further information on their condition.

Rutte said during a trip to Warsaw that he had heard of the deaths of four soldiers and was thinking about their families, as well as of the United States.

Rutte told reporters in Warsaw: “This news is tragic. We send our condolences to their loved ones and families. “

A statement from U.S. Army Europe and Africa public affairs in Wiesbaden, Germany, said the soldiers were conducting scheduled tactical training at the time.

LRT, the Lithuanian public broadcaster, reports that four U.S. soldiers and a vehicle have gone missing during an exercise at General Silvestras Zukauskas’ Training Ground in Pabrade. Pabrade lies less than 10km (6 miles) from the Belarus border.

Since Belarus declared its independence in 1990, the Baltic countries of Lithuania, Latvia, and Estonia (all NATO members) have had chilly relationships with Russia.

Gitanas Nusea, the Lithuanian President, is one of those who has been most vocal in supporting Ukraine’s struggle against Vladimir Putin and his forces.