US marines in 1975 during the Vietnam war: Vietnamese officials said they will open three previously restricted sites to US investigators. Photograph: Henri Huet/AP

The Vietnamese government has agreed to open three new sites for excavation by the US to search for troop remains from the war in the 1960s and 70s.

The announcement came as the US defence secretary, Leon Panetta, and the Vietnam defence minister, Phuong Quang Thanh, exchanged artefacts collected during the war: letters written by a US soldier who was killed that had been kept and used as propaganda, and a diary belonging to a Vietnamese soldier. An American service member took the journal back to the US.

American officials have said this is the first joint exchange of war artefacts. The two defence 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 the Pentagon believes will help locate troops missing in action.

The letters were written by Sergeant Steve Flaherty of the 101st Airborne, from Columbia, South Carolina, who was killed in South Vietnam in March 1969. According to defence officials, Vietnamese forces took Flaherty's letters and used them in broadcasts during the war.

A Vietnamese colonel, 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.

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

The small maroon diary belonged to Vu Dinh Doan, a Vietnamese soldier who was killed in a machine gun fight, according to defence officials. Officials said that a marine, Robert "Ira" Frazure of Walla Walla, Washington, saw the diary – with a photo and some money inside – on the chest of the dead soldier and took it back to the US.

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 programme History Detectives. The show then asked the defence and state departments to help return the diary.

Source: guardian.co.uk