Story highlights Areas of Vietnam remain contaminated by the herbicide Agent Orange

The U.S. military used the toxic chemical during the Vietnam War

It can cause cancer, birth defects and other health problems

The U.S. government is working on a cleanup project in Vietnam for the first time

The United States has pitched in for the first time to clean up part of the toxic legacy left by the millions of gallons of the chemical compound codenamed Agent Orange that it dumped on Vietnam during the war there in the 1960s and '70s.

The U.S. military used Agent Orange to kill trees and plants that blocked visibility from the air during the Vietnam War. But the chemical was contaminated with dioxin, which can cause cancer and birth defects. It harmed humans and left areas of Vietnam contaminated.

In an effort to start addressing this noxious remnant of the war, the U.S. and Vietnamese governments, along with partnering organizations, are treating a contaminated zone at the airport of the central Vietnamese city of Danang.

Workers will dig up soil, stockpile it, and treat it using high temperatures that break down the dioxin.

"We are both moving earth and taking the first steps to bury the legacies of our past," David Shear, the U.S. ambassador to Vietnam, said Thursday at a ceremony opening the project at the airport. He described the effort as "a historic milestone" for the relationship between the two countries.

Led by the U.S. Agency for International Development and the Vietnamese Ministry of National Defense, the cleanup in Danang aims to reclaim an area of 29 hectares.

It will cost an estimated $43 million, and is expected to finish in 2015, according to the Vietnamese Embassy in Washington . U.S. officials had no immediate comment on the cost and timetable of the project.

Agent Orange is "one of the most toxic compounds known to humans," according to the United Nations.

The use of the chemical by the U.S. military in Southeast Asia between 1961 and 1971 devastated large swathes of the Vietnamese countryside and affected millions of people.

As many as one million people in Vietnam have disabilities or other health problems associated with Agent Orange, the Vietnamese Red Cross has estimated, citing local studies.

About 2.6 million U.S. military personnel are believed to have been exposed to the chemical, according to the Department of Veteran Affairs.

Hundreds of thousands of Vietnam veterans are estimated to be alive and eligible for treatment for Agent Orange-related illnesses, the department says. It has compiled a list of health problems believed to be associated with exposure to Agent Orange, including cancer, Parkinson's and a type of heart disease.

The Vietnamese government has underscored the need to "pursue efforts to overcome the aftermath of toxic substances left by the war" in other areas around the country, according to the Vietnamese Embassy in Washington.

The U.S. government is planning to carry out an environmental assessment of another contaminated area -- in Bien Hoa, southern Vietnam -- in coordination with the Vietnamese government , the United Nations and others, Shear said Thursday.