The powder was mailed with an intimidating leaflet from an unknown group called Jemaah Muhajirin Mohamad, demanding Washington remove its troops from Iraq "or face the consequences." It threatened to blow up the embassy and kill or kidnap Americans in Malaysia, said Abdul Aziz Bulat, Kuala Lumpur's police chief of criminal investigations.
"We think that it's just a hoax and this group is nonexistent, but we will take precautions by investigating this seriously," Abdul Aziz told The Associated Press.
Police, firefighters and a medical crew rushed to the embassy Monday after staff there opened the letter, he said. The letter was mailed from within Malaysia.
Three embassy staff members exposed to a yellowish substance in the envelope were briefly quarantined for a medical checkup, which cleared them, district police official Aman Hussain said.
The powder was sent for laboratory tests to determine whether it might contain anthrax spores or other toxins, Aman said.
Prime Minister Abdullah Ahmad Badawi said preliminary investigations showed the substance wasn't anthrax.
A week ago, the U.S. Embassy in Colombo, Sri Lanka, was closed after receiving mail containing a suspicious powder. Tests found the powder harmless.
Frank Whitaker, the U.S. Embassy's spokesman in Kuala Lumpur, said the embassy remained open and operations resumed normally.
Malaysia — a moderate, predominantly Muslim nation that staunchly opposed the U.S.-led invasions of Iraq and Afghanistan — is considered one of Asia's most peaceful, stable countries.
Since 2001, the Malaysian government has arrested more than 70 suspected members of the al Qaeda-linked Jemaah Islamiyah regional terror network, which has been accused of various plots and deadly bombings, including the 2002 Bali blasts in Indonesia that killed 202 people.
In the United States, anthrax-laced envelopes were mailed in fall 2001 to government offices and news media. Five people, including 94-year-old Ottilie Lundgren of Oxford, Conn were killed and 17 fell ill, further rattling a nation on edge after the Sept. 11 terrorist attacks.
Earlier this month, FBI agents investigating the 2001 U.S. anthrax attackswho, days after the first anthrax mailings, had applied for a patent for a system to identify chemical and biological attacks.
Anthrax is caused by bacteria that can be passed from livestock to humans. The disease can affect the skin, the lungs or the digestive system. When treated appropriately, less than one percent of people with the cutaneous, or skin form, of anthrax die. But more than half of those who contract inhalation or gastrointestinal anthrax perish.