Canadian police have begun an investigation after a yet-to-be identified woman in Canada allegedly sent a letter containing the poison ricin to U.S. President Donald Trump.

“Our Chemical, Biological, Radiological, Nuclear, Explosives team (CBRNE) is leading the operation. Police and Fire teams from Longueuil are also on site. All necessary measures have been taken to ensure public safety,” said a tweet by the Royal Canadian Mounted Police (RCMP) on Monday.

The woman was reportedly arrested at the Canadian-U.S. border and was expected to appear in court later in the afternoon in Buffalo, the United States, facing federal charges in the United States.

The RCMP said a police operation is ongoing at a residential street located south of Montreal.

Media reports said the letter was intercepted after being sent to Washington from Canada.

Officials said it was intercepted at a government facility that screens mail addressed to the White House and President Donald Trump.

Both police and media reports have not yet indicated whether the suspect is Canadian.

*Reported by Xinhua