Gregg Bourland, chairman of the Cheyenne River Sioux tribe in South Dakota, told politicians that Native Americans were some of the first victims of what would today be called bio-terrorism.

According to Mr Bourland, the British were the worst offenders, using smallpox-laced blankets to infect tribal members at Fort Pitt, on the Pennsylvania frontier, in 1763.

“We have zero resistance to this disease,” Mr Bourland said in an interview with The Times. “That’s why the vaccination is so critical to Native Americans. We just want to be protected.”

He rejects claims that the vaccine itself can be fatal, saying that his grandmother’s generation were all inoculated against the disease in the 1930s and none of the tribal members died.

One of the millions of American Indian victims of smallpox was Mr Bourland’s great-great-grandmother, who was called Blue Earrings.

Senator Tom Daschle, whose office was the target of an anthrax attack after September 11, has promised to make Mr Bourland’s case to senior health officials. Other American politicians, however, have not replied to the tribal chief’s request for help.

At present the Bush Administration plans to make the smallpox vaccine available to the entire population of the United States within five days of a biological attack.

Mr Bourland estimates that there were 60 million Native Americans when Christopher Columbus unintentionally discovered them in October 1492. The explorer initially mistook the native population for Indians, hence their name.

When relations between the natives and the settlers broke down, smallpox turned out to be the most effective weapon against them, even though in most cases the highly contagious viral disease was not spread deliberately. Today, there are only two million Native Americans.

Unlike the Europeans, the Native Americans did not build up immunity against the disease, which can be fatal when it leads to an infection of the lungs, heart or brain. The disease is particularly horrific because of the distinctive rash that it produces.

Allegations that the British used smallpox as a biological weapon against the Native Americans came after an incident in 1763, at the end of the French and Indian Wars.

The apparent mastermind of the attack was Sir Jeffrey Amherst, also the 1st Baron of Montreal, who was considered a hero in London for leading the defeat of the French in Canada. Sir Jeffrey allegedly “weaponised” the smallpox disease by giving Chief Pontiac’s forces blankets that had been used by British smallpox victims.

A letter written by Sir Jeffrey to an unidentified subordinate suggests that the attack was deliberate. “I may try to inoculate the Indians by way of blankets,” he wrote, “taking care, however, not to get the disease myself.” Sir Jeffrey, who later became Commander-in-Chief of Britain’s forces in North America, said that he wished he could have just set dogs on them instead.

The letter was preserved by the US Library of Congress as part of the British Manuscript Project undertaken during the Second World War.

According to some historians, the British Army deliberately exposed its own troops to a mild form of smallpox. The soldiers who recovered from the disease then had lifelong immunity.

Other historians have questioned whether the British would have known enough about germs to launch a deliberate biological attack. “I am unable to see where Amherst hatched such a diabolical plot, let alone put it in motion,” Peter Landry, a Canadian lawyer and historian who has written about Sir Jeffrey, said. “Those who write that he did should be called upon to provide some authority for the proposition.

“I know that contagious diseases of the European variety did get into the Indian population in 1746, but this is because they helped themselves to the clothing and blankets of dead French soldiers.”

Mr Bourland, however, said that there was no doubt that the British used smallpox as a weapon. “Whether or not it could be called bio-terrorism, the effect was the same,” he said.

In spite of the allegations of germ warfare, Sir Jeffrey — who was made a field marshal in 1778 and then 1st Baron Amherst of Montreal in 1797 — returned to Britain a hero.

Chronicle of a silent killer