Vietnam and the United States kicked off a joint effort Friday to clean up sites contaminated by Agent Orange, a dangerous chemical defoliant used during the two countries' war which ended in 1975.

The U.S.-funded operation aims to remove all unexploded ordnance around a former American air base at Danang. U.S. officials say once the unexploded weapons are gone, teams will begin cleaning the soil to remove any traces of Agent Orange, which contains dioxin, a substance that can cause birth defects, cancer and other health problems.

The U.S. military sprayed millions of liters of Agent Orange over Vietnam's jungles in the 1960s, to remove vegetation and make it easier to find North Vietnamese forces. Vietnamese officials have estimated that 3 million people suffer from health problems the chemical agent caused.

Relations between the two former enemies have been gradually warming since formal ties were established 16 years ago, but the Agent Orange issue has been a lingering irritant, with Vietnam demanding compensation. The U.S. agreed to clean up sites the Vietnamese government considers highly contaminated, starting with 29 hectares of contaminated land at the Danang air field.

The U.S. has allocated $32 million for the effort.