South Korean environmentalists clean up after performing during a rally in front of the US embassy in Seoul May 23, 2011, where they demanded an investigation into claims by US veterans who said they were ordered to dump the toxic chemical defoliant Agent Orange at Camp Carroll, in the southeastern part of South Korea, in the late 1970s.[Photo/Agencies]

SEOUL -- The US military in South Korea said Monday it had made "some progress" in its investigation into allegations that large amounts of the toxic defoliant Agent Orange were buried over 30 years ago at a US military base in the country.

"While we are not sure that what we've found directly correlates to the claims made in the media, we have discovered information about materials buried on Camp Carroll in 1978," said Lt. Gen. John D. Johnson, commander of the Eighth Army, in a press release.

The Eighth Army has conducted a review of its military records and reports to probe the allegations made by three US veterans, who told a US television station last week that they helped bury the toxic chemical at Camp Carroll, located some 300 kilometers southeast of Seoul, in 1978.

A 1992 Army Corps of Engineers environmental assessment found that a "large number of drums containing chemicals, pesticides, herbicides and solvents" were buried at the base, according to the press release. The study, however, did not say if Agent Orange was among those chemicals, it said.

The study added that the chemicals and between 40 and 60 tons of soil were removed in 1979 and 1980 and disposed of offsite.

"Eighth Army officials are still trying to determine why the materials were buried and how it was disposed after it was excavated," the release said.

South Korea and the United States agreed over the weekend to launch a joint investigation into the alleged dumping of the toxic chemical.

The news prompted Seoul's environment ministry to send last week a team of officials and experts to the site to check soil and underground water around the camp.