Arrest made at U.S.-Canada border in White House ricin envelope investigation

WATCH: What is ricin poison sent to the White House?

A person who was trying to enter the U.S. from Canada has been arrested in connection with an investigation into a ricin-laced envelope addressed to the White House.

Several sources tell Global News that the final determination is still being made on her citizenship as the arrested woman was classified as a U.S. person — someone who has either had American immigration status now or in the past or is an American citizen.

The sources previously told Global News Sunday evening that senior officials believed she was a American citizen, and confirmed that she was carrying a gun when she was arrested.

The arrest was made at the Peace Bridge in Buffalo, N.Y., Aaron Bowker, a public affairs liaison with U.S. Customs and Border Protection, confirmed.

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A spokesperson for the FBI said the police force has arrested “an individual allegedly responsible for sending a suspicious letter.”

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The news comes a day after the RCMP confirmed it received a request from the FBI to assist with the investigation into the letter.

According to the RCMP, FBI analysis of the envelope indicated the presence of ricin, a potentially lethal poison derived from castor beans.

“Initial information from the investigation suggests that the letter originated in Canada,” an RCMP spokesperson said in a statement Saturday.

Click to play video: '‘I will not live in fear’ says Sen. Susan Collins after husband receives letter said to contain ricin'
‘I will not live in fear’ says Sen. Susan Collins after husband receives letter said to contain ricin

The envelope was intercepted at a government facility that screens mail addressed to the White House and the U.S president, a law enforcement source told the Associated Press.

AP reported Sunday, citing three law enforcement officials, that the woman is expected to face federal charges.

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An initial court appearance is scheduled for Monday.

Two years ago, envelopes containing the substance from which ricin is made were sent to U.S. President Donald Trump and members of his administration.

Ricin-laced letters were also sent to then-president Barack Obama twice in 2013.

On Saturday, a spokesperson for Public Safety Minister Bill Blair office said they were aware of reports saying packages containing ricin had been sent to  U.S. federal government sites.

“Canadian law enforcement is working closely with their U.S. counterparts. As this is an active investigation we cannot comment further.”

–With files from The Associated Press and Global News’ Mercedes Stephenson

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