An envelope containing a poison, ricin, was intercepted during the week by the security services of US President Donald Trump.
A suspect, a woman who carried a gun, was arrested on Sunday near the Canadian border.
A suspect has been arrested after sending an envelope containing poison, ricin, and addressed to US President Donald Trump, authorities said on Sunday.
"I confirm that an arrest was made at the Peace Bridge in Buffalo, New York," Customs official Aaron Bowker told AFP in reference to a bridge that links Canada to New York State .
"The investigation is ongoing," he added.
The suspect is a woman who was carrying a gun when she was arrested, according to US media.
A government official told AFP, on condition of anonymity, that a court appearance was scheduled for Monday.
Ricin, a deadly poison without antidote
The American press had let it be known on Saturday that the authorities had intercepted an envelope containing ricin and addressed to Donald Trump.
The letter had been discovered earlier in the week and had not made it to the White House, according to the New York Times daily and CNN television.
The newspaper claims the letter was mailed from Canada.
Mail addressed to the White House is first inspected and then sorted in depots near Washington.
According to CNN, the contents of the envelope were tested several times in one of these repositories, with confirmation of the presence of ricin.
Ricin, which is produced by processing castor beans, is fatal even in tiny doses if swallowed, inhaled, or injected, causing organ failure.
There is no antidote.