Recent reports in the South Korean media revealed for the first time that the defoliant had been secretly deployed outside the Vietnam War theatre.

Seoul has admitted that thousands of its soldiers were involved in hand-spraying toxic defoliants, including Agent Orange, along the demilitarised zone (DMZ) separating the two Koreas.

They did so in order to kill foliage that was providing cover for potential North Korean infiltrators.

Agent Orange spraying in Vietnam

But the South Korean Government says the operation was only conducted because the US had requested it.

Washington, however, says the decision was made in Seoul.

"(We) presume that the toxic defoliants were used after the US troops first asked for it and then Korean troops perceived the need," the South Korean Defence Ministry said in a statement.

It said US troops stationed in South Korea received approval to use defoliants - blamed for causing cancer in US and Korean soldiers - after consultation with the Korean Government through the US State Department.

Inquiry

But the US argues that the use of Agent Orange to clear the DMZ was not taken on its initiative, and says there is no evidence of a cover-up.

"The records are clear that that was a decision made by the South Korean Government and military at that time," Rear Admiral Craig Quigley told a Pentagon briefing on Tuesday.

But he did concede that research into the use of defoliants had been "spotty", and that the issue "had fallen off people's scopes for a long period of time".

South Korea's defence minister has ordered an inquiry into the matter.

"If the investigations prove the injuries, the government would seek proper measures according to the law to support those who were exposed to defoliants," the ministry statement said.

Agent Orange was widely used by US forces during the Vietnam War and has been linked to cancers of the lymph glands, lungs and skin, as well as congenital birth defects.