Four US Army members have died in Lithuania after they disappeared on a training site while on maneuvers just miles from the border, NATO’s Secretary-General Mark Rutte said Wednesday.

The four soldiers from the 1st Brigade, 3rd Infantry Division, based out of Fort Stewart, Georgia, were last seen alive on Tuesday riding an armored vehicle during tactical training exercises at a military site near the city of Pabrade, in eastern Lithuania.

The area is about six miles from the border with Belarus — a staunch Russian ally, Army officials said.

Rutte said he had received word of the deaths of the four soldiers and extended his thoughts and prayers to their families and the United States.

“This is still early news so we do not know the details,” he told reporters while on a visit to Poland’s capital, Warsaw. “This is really terrible news and our thoughts are with the families and loved ones.” (Read more from “4 U.S. Soldiers Killed After They Went Missing on Training Mission in Lithuania Just Miles From the Border” HERE)