WASHINGTON, May 12: The most extensive bio-terrorism drill in US history began on Monday, with officials handling an imaginary radioactive attack in Seattle and handling a fake threat of a pneumonic plague in Chicago that spreads to Canada.

The five-day drill, spearheaded by the Department of Homeland Security, will cost 16 million dollars and involve more than 8,500 people from 100 federal, state and local agencies, the American Red Cross and the Canadian government.

The scenarios involve two attacks — one radioactive, one biological — by two cells of a terrorist group.

The drill started in Seattle, where officials responded to a fake explosion causing more than 100 casualties. Under the scenario, radiation will be detected near the blast’s crater, triggering a response from federal officials.

The drill in Chicago starts on Tuesday, when “patients” will show up at hospitals suffering from flu-like symptoms. In the script, the terrorist group had released a deadly plague in aerosol form on Saturday.

More cases were to be reported across the nation and in Vancouver, Canada.

Plague, especially pneumonic plague, is a “Category A” agent on the US government’s list of likely biological weapons.

A detailed, 200-page scenario has been written for the drill, which officials said will be as realistic-looking as possible. Stand-ins will portray President Bush, Vice President Dick Cheney and even press secretary Ari Fleischer.