U.S. and South Korean investigators say their probe has so far turned up no evidence that Agent Orange was dumped at a U.S. military base in South Korea decades ago.

The investigators announced last week that they had identified “anomalous areas” under a helipad at Camp Carroll in South Korea that reports said could be metallic objects or barrels. But in a press release Wednesday, the investigators stressed that the anomalies could also be caused by water or differences in soil composition or density.

The investigating team said it is now conducting core sampling at various locations to further identify the anomalies. The investigation was launched after a military veteran in the United States said he remembered being ordered to bury hundreds of liters of the highly toxic defoliant at the base between 1963 and 1964.

Investigating teams have also been examining the site of Camp Mercer, a former U.S. military base outside the capital, Seoul. South Korea's Yonhap news agency quotes U.S. officials saying the chemical was buried in the 1960s but was removed and shipped out of the country in the late 1970s.

North Korean media have been trying to take advantage of the controversy for propaganda purposes. Rodong Sinmun, the official newspaper of North Korea's ruling Workers' Party, last week accused the South Korean government of failing to protest the “slack investigation” of the dumping by U.S. officials.