A Canadian woman has pleaded guilty to biological weapons charges after sending former President Donald Trump a letter laced with deadly ricin poison.

The envelope was intercepted in September 2020 before ever being delivered to the White House.

The FBI found the fingerprints of Pascale Ferrier, 55, on the letter, which urged Mr Trump to drop out of the presidential race.

Ferrier is expected to be sentenced in April to just under 22 years in prison.

Ferrier, a dual citizen of France and Canada, was arrested crossing the border into Buffalo, New York in September 2020. She was carrying a gun, knife and rounds of ammunition.

She placed the toxin into an envelope containing a letter she wrote to the former president at the White House.

"I found a new name for you: 'The Ugly Tyrant Clown'," she wrote in the letter to Mr Trump, according to FBI charging documents filed in 2020.

She mailed similarly tainted letters to eight Texas law enforcement officials at the same time. Ferrier has pleaded guilty on separate criminal charges related to those as well.

In 2019, Ferrier was detained in the state for about 10 weeks for unlawfully carrying a weapon and driving without a valid licence, and she blamed those officials for that detention, according to a US justice department statement.

There is no known antidote to ricin. Depending on the dose, it can cause death within 36 to 72 hours, according to the US Centers for Disease Control and Prevention.

In 2014, a Mississippi man was sentenced to 25 years in prison after sending ricin laced letters to President Barack Obama and other officials.

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