U.S. Navy divers are pushing through mud in a flooded Lithuanian bog in an effort to excavate a submerged armored vehicle and locate four missing U.S. soldiers, Army officials said.

Hundreds of troops and emergency workers are racing to find four US soldiers who went missing during a training mission near Lithuania’s border with Belarus, the US Army said Thursday, after their armored vehicle was found submerged in a body of water.

Four U.S. soldiers who went missing while training in Lithuania have died, NATO Secretary-General Mark Rutte said Wednesday. Speaking to reporters during a trip to Warsaw, Rutte said he had received word of the deaths of the four American troops.