Authorities are testing a suspicious powder mailed to the U.S. Embassy in Malaysia to determine whether it is anthrax, officials said Monday after the second such scare at a U.S. mission in Asia within a week.

The powder was mailed with an intimidating leaflet from an unknown group called Jemaah Muhajirin Mohamad (search), 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, Abdul Aziz 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.

A week ago, the U.S. Embassy in Colombo, Sri Lanka (search), 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 (search) — 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 (search) regional terror network, which has been accused of various plots and deadly bombings, including the 2002 Bali (search) blasts in Indonesia that killed 202 people.