Undercover Thai police, tipped off by U.S. investigators, on Friday arrested a man Friday trying to sell them radioactive material that could be used to make so-called "dirty bombs."

Police did not say if the man was suspected of having terrorist connections, and U.S. officials said the material was not destined for weapons against Americans, as originally suspected.

The arrest came after three alleged Islamic terrorists were arrested this week in southern Thailand, accused of plotting bombings of embassies and tourists spots here. The men are alleged members of Jemaah Islamiyah (search), the terror group blamed for last year's nightclub bombings on the Indonesian island of Bali (search).

In Friday's sting operation, Thai police met Narong Penanam, 44, in the parking lot of a Bangkok hotel, where he gave them a metal container that he said contained uranium, police Col. Pisit Pisutisak said.

Narong — who said he got the material from neighboring Laos and that his contacts there had more — was expecting to sell it for $240,000.

An analysis of the material revealed it was not uranium but the industrial material cesium-137 (search), suitable for making dirty bombs, which spread radioactive chemicals over a wide area.

Narong was charged with illegal possession of nuclear materials, punishable by up to a year in prison and a fine of $240.

The U.S. Customs Service initiated the investigation and had agents present during the arrest, a U.S. Embassy spokesman said on condition of anonymity.

Gary Phillips, assistant customs attache at the U.S. Embassy, told the Thai television station ITV that "originally, we were told it was going to be used against the United States, but we substantiated that that was not true."

No other details about the investigation or the suspect were immediately available.