Cambodian authorities said Thursday they were still seeking an unspecified number of suspected terrorists after foiling an apparent attempted plot to bomb the capital's upcoming Water Festival.

The claims came after authorities announced they had already arrested and were now holding six men at an undisclosed location after charging them with terrorism-related offences.

Interior Ministry spokesman Khieu Sopheak said he could give few details regarding the ongoing investigation, except to say that the men in detention were not the ringleaders.

More than 1.5 million people are expected to stream into the capital for the annual festival starting Saturday, which features three days of boat races presided over by King Norodom Sihamoni and celebrates the end of the monsoon season. This year boats from Thailand and Vietnam will also compete.

"We are still seeking the ringleaders," General Sopheak said by telephone, urging calm. "The actual plan looks like a fantasy. The Khmer Rouge had a stronger system than this and we broke them."

He said all the men except one were members of the Kampuchea Krom ethnic group and all had previous criminal records as petty thieves and cattle rustlers and were likely just the tools of more organized leaders. He declined to comment on local media reports that at least one other suspect had fled into neighbouring Thailand.

Sopheak also declined to comment on the methods, targets or motives police suspected in connection with the alleged planned attacks until further investigations had been conducted.

The men were arrested Tuesday in a sweep which covered the northern province of Siem Reap, the Thai border province of Banteay Meanchey, Kandal province, which borders the capital, and Svay Rieng province bordering Vietnam. They were charged Wednesday in Phnom Penh Municipal Court.

Police sources speculated that the group may have been attempting to disrupt the festival to protest Vietnam's control of the Mekong Delta area and hit out at the Cambodian government. The dominant Cambodian People's Party is seen as having close ties to the Vietnamese government.

The term Kampuchea Krom literally translates as "Khmer from below," referring to the lower areas of the Mekong Delta where the majority of the indigenous ethnic Khmer minority live in southern Vietnam.

The Kampuchea Krom areas were awarded to Vietnam when independence was granted from France in 1954. In the 1970s, the Khmer Rouge repeatedly attacked Vietnam in an attempt to take back those areas of the delta. These attacks in part led to Vietnamese-backed troops overthrowing the Khmer Rouge in 1979 and installing a government sympathetic to Vietnam.

Kampuchea Krom groups have repeatedly called for independence from Vietnam and claimed human rights abuses.

The arrests come six years after the November 2000 attempted coup by members of the Cambodian Freedom Fighter (CFF) terrorist movement, but authorities said there was nothing to indicate that the two groups were linked in any way.