HANOI, Vietnam (AP) -- The Vietnamese government on Monday agreed to open three new sites in the country for excavation by the United States to search for troop remains from the war, the minister of defense told U.S. Defense Secretary Leon Panetta during a meeting here.

The announcement came as Panetta and Vietnam Defense Minister Phuong Quang Thanh exchanged artifacts collected during the war - letters written by a U.S. soldier who was killed that had been kept and used as propaganda, and a small maroon diary belonging to a Vietnamese soldier. A U.S. service member took the journal back to the U.S.

U.S. officials said this is the first time such a joint exchange of war artifacts has occurred. The two defense leaders agreed to return the papers to the families of the deceased soldiers.

During the meeting with Panetta, Vietnamese officials said they would open the three previously restricted sites that the Pentagon believes are critical to locating troops missing in action.

The letters were written by U.S. Army Sgt. Steve Flaherty, who was from Columbia, S.C. and was with the 101st Airborne. He was killed in the northern section of South Vietnam in March 1969. According to defense officials, Vietnamese forces took Flaherty's letters and used them in broadcasts during the war.

Vietnamese Col. Nguyen Phu Dat kept the letters, but it was not until last August, when he mentioned them in an online publication, that they started to come to light.

Early this year, Robert Destatte, a retired Defense Department employee who had worked for the POW/MIA office, noticed the online publication, and the Pentagon began to work to get the letters back to Flaherty's family.

The small diary belonged to Vu Dinh Doan, a Vietnamese soldier who was found killed in a machine gun fight, according to defense officials. Officials said that a Marine, Robert "Ira" Frazure of Walla Walla, Wash., saw the diary - with a photo and some money inside - on the chest of the dead soldier and took it back to the U.S.

The diary came to light earlier this year when the sister of a friend of Frazure's was doing research for a book and Frazure asked her help in returning the diary. The sister, Marge Scooter, brought the diary to the PBS television program History Detectives.

The show then asked the Defense and State departments to help return the diary.