(Reuters) – A woman arrested by U.S. authorities on suspicion of sending a ricin-filled envelope to the White House and to five other addresses in Texas will appear before a federal court in Buffalo, New York, later on Tuesday.

U.S. authorities arrested a woman on the Canada-U.S. border on Sunday, at the so-called Peace Bridge that runs between Fort Erie, Ontario, and Buffalo.

She is due to make her initial appearance at U.S. District Judge H. Kenneth Schroeder Jr. at 4 p.m. EDT (2000 GMT). She has yet not been officially identified.

The envelope was intercepted at a government mail center before it arrived at the White House, Canadian police said on Saturday.

Canadian police on Monday searched an apartment in a Montreal suburb linked to the woman. She has joint Canadian and French citizenship, two sources said.

The woman is suspected of sending a total of six letters, with the other five addressed to law enforcement and detention facilities in South Texas, according to a U.S. law enforcement source.

So far no links to political or terrorist groups have been found, but the investigation is ongoing, the source said.

The police department in Mission, Texas, received a suspicious letter within the last week, Art Flores, a spokesman for the department, said on Monday. The department did not open the envelope and turned it over to the FBI, he said.

Flores also said the Mission police had arrested the woman now believed to be held in Buffalo in early 2019.

Ricin is found naturally in castor beans but it takes a deliberate act to convert it into a biological weapon. Ricin can cause death within 36 to 72 hours from exposure to an amount as small as a pinhead. No known antidote exists.

(Reporting by Christinne Muschi in Longueuil, Steve Scherer in Ottawa and Mark Hosenball in Washington, additional reporting by David Ljunggren in Ottawa, writing by Steve Scherer; Editing by Jonathan Oatis)