Scientists from the United States and Vietnam have begun measuring levels of cancer-causing dioxin at a site where Agent Orange was stored during the Vietnam war.

Researchers visited the central Vietnamese province of Danang a few days ago to begin testing new methods of measuring toxic dioxin in the soil of a former U.S. military base. The base is one of about 30 dioxin hot spots around Vietnam where the defoliant Agent Orange was spilled or heavily sprayed.

The trip marks the first time U.S. and Vietnamese government scientists have worked together in field studies on Agent Orange. The test results should be available within six months.

The announcement came during a groundbreaking joint conference this week to share information on how much damage Agent Orange has done to Vietnam's people and environment.

It is one of the most sensitive issues in relations between the former enemies. The U.S Air Force sprayed about 70 million liters of the herbicide during the war, trying to dissolve jungle cover for the North Vietnamese forces that eventually won the country's civil war.

Agent Orange contains dioxin, which has been proven to cause cancer and birth defects. But it remains unclear exactly how widespread the health damage to the Vietnamese people is.

Hanoi claims more than one million people are victims of Agent Orange, and seeks U.S. aid to help them. But Washington believes that figure is inflated, and says further study is needed to find out the real damage.