Final test results have confirmed that a suspicious powder found in a U.S. Senate office building is the poison, ricin.

The chief of the U.S. legislature's police force, Terrance Gainer, Tuesday announced the results of the tests on the white substance found in a Senate Office building a day earlier. "Tests have confirmed that this is ricin," he said.

The discovery of the white powder in the mailroom of Senate Majority Leader Bill Frist's office forced the closure of three Senate office buildings and the cancellation of numerous Senate hearings on President Bush's new budget.

But the Senate was nevertheless in session, as was the House.

Senator Frist, who is also a medical doctor, said 16 people were on the fourth floor of the Dirksen building where the powder was discovered. He said there is no indication that anyone's health was affected by the contamination.

Senator Frist said it is premature to rule out whether the incident is linked to terrorist activity. "The question is whether it is a criminal act or a terrorist act. In my mind they are both the same. We know this was sent specifically to the United States Senate, to an individual. Because it is a poison, a toxic chemical, that we know is deadly, that we know there is no treatment for that, the assumption is that it is the intent to do harm. Because of the nature of the agent, it is meant to terrorize as well," he said.

Police Chief Gainer said an investigation has begun with assistance from a joint terrorism task force and the Federal Bureau of Investigation.

Senate Sergeant-at-Arms William Pickle says he hopes all Senate office buildings will be reopened within the next week, depending on the progress of the investigation.

Meanwhile, a suspicious powder found at a post office in Connecticut Monday is undergoing testing. The substance, found in an envelope addressed to the Republican National Committee, was discovered at the same facility where anthrax spores were found in 2001. A series of anthrax-tainted letters were mailed to locations in the eastern United States that year, including to Senators Tom Daschle and Patrick Leahy. Five people died. No one has been arrested in those incidents.