Ricin find closes three Senate buildings

Three US Senate office buildings remained closed on Wednesday after a white powder determined to be Ricin was found in the office of Senate Federal Majority leader Bill Frist.

Senator Frist called it 'an act of terrorism'. He said that no one has been taken ill in the Senate mailing.

"Because it is a poison, a toxic chemical that we know is deadly, that we know there is no treatment for," said Frist, "the assumption is that it was sent with the intent to harm. Because of the nature of the agent, it is clearly intended to terrorise as well."

He said it was premature to conclude that any terrorist group such as the al Qaeda had been involved.

The deadly poison, which has no antidote or cure was found on Tuesday in the mailroom of Frist. The Federal Bureau of Investigation and the police are trying to find the source of Ricin and have yet to make any arrests.

The police stood guard on streets around office buildings. Frist said a Senate staff member spotted the Ricin on an automatic mail opener where about 30 letters had been opened. The staffer asked everyone to leave the room and called the Capitol Police.

Most of the letters, according to senate staffers, were from Frist's constituents in Tennessee.

Dozens of Senate workers were being monitored and health officials urged the staff to look out for swiftly developing fever, coughs or fluid in the lungs over the next two or three days.

The postal facility that processes Congress' mail was also shut. The investigation into the letter continues and there have been no arrests, officials said.

The discovery of the deadly poison Ricin on Capitol Hill on Tuesday brought a chilling reminder of the October 2001anthrax attacks, which remain unsolved. The anthrax incident closed several postal facilities in the capital for several weeks.

Frist, a medical doctor, noted that mail to congressional offices has been irradiated since the October 2001 anthrax attacks but that radiation would be unlikely to have an effect on Ricin.

This was the second toxic attack on the US Capitol -- seat of the Senate, House of Representatives and several offices -- in two and a half years.

A Justice Department official revealed last night that a letter containing Ricin was sent to the White House in November, but it was intercepted at a small mail handling centre off the White House grounds. The White House has been silent on that episode.