AN American postal worker was today "gravely ill" after contracting the most deadly strain of anthrax.

He is the ninth person in the US to be diagnosed with anthrax - but only the third to contract the inhalation form of the disease.

The victim worked at a Washington postal centre where mail for the US Congress is sorted.

Five colleagues in Washington are also showing possible symptoms and a further 2,200 postal staff in the city are being tested.

US President George Bush has declared that sending anthrax through the post is "an act of terror".

In his weekend US radio address, Mr Bush said: "We do not yet know who sent anthrax to the United States Capitol or several different media organisations.

"We do know that anyone who deliberately delivers anthrax is engaged in a crime and an act of terror."

One person has so far died from the disease. British-born Florida journalist Bob Stevens also contracted the inhalation form of anthrax.