Nine senior Israeli underworld figures were under arrest Thursday on suspicion of smuggling and distributing thousands of pills containing a life-threatening substance, police said. A gag order was imposed on the case, but police said the added dangerous ingredient was the same substance contained in a defoliant used by the US during the Vietnam War. Eli Korland from the Central District Police Investigations Unit said 48,000 Ecstasy pills had been found, of which 3,000 were contaminated with the lethal substance. He said police suspected that many more of the pills had been distributed but that the detainees were refusing to cooperate with police. He said the pills appeared identical to regular Ecstasy pills and urged the pubic to stay well away from them. Police described the pills as florescent green and etched with smiley faces. The affair came to light after an Israeli and three Japanese were arrested in the Netherlands in possession of the pills. Those arrests were made following an investigation lasting several months and intelligence transferred to Dutch police by Israeli detectives. A member of the Israel Police's Central District Investigations Unit was sent to Holland to collect a sample of the pills for analysis. It was discovered that some of the pills contained a lethal ingredient. On Monday, eight more people were arrested in central Israel on suspicion of involvement in the smuggling operation; their remands were extended for seven days. Police searched the suspects' homes and found large amount of cash, cellphones, plane tickets and incriminating documents. They also seized four vehicles. Police said the pills were being sold in Israel, Thailand and Japan, mainly in nightclubs, and that more arrests were expected. Two people exposed to the substance in Israel in the past died, but it was unclear if the deaths were linked to the pills now being distributed.