OSLO (Reuters) - Four U.S. soldiers were injured in a major North Atlantic Treaty Organization exercise in Norway in an accident involving four vehicles on Tuesday, the U.S. military said.

One soldier was shortly released after being hospitalized, and the three others are under observation in stable condition, the U.S. Joint Information Center said in a statement.

The soldiers were in trucks delivering cargo to Kongens Gruve, Norway, in support of Trident Juncture 18, the biggest NATO exercise in recent years, two days ahead of the start date.

Trident Juncture 18 will involve around 50,000 personnel from NATO Allies and partner countries, about 250 aircraft, 65 vessels and up to 10,000 vehicles. It will take place from Oct. 25 to Nov. 7 in central and eastern Norway, the surrounding areas of the North Atlantic and the Baltic Sea, including Iceland and the airspace of Finland and Sweden.

“The accident occurred when three vehicles collided and a fourth vehicle slid off the pavement and overturned while trying to avoid the three vehicles that had collided,” the information center said.

The vehicles and personnel in the accident were assigned to the U.S. Army’s 51st Composite Truck Company stationed in Baumholder, Germany.

The U.S. military is working with Norwegian authorities to investigate the accident.