US authorities have arrested a man from the the U.S. state of Mississippi suspected of sending a poisoned letter to U.S. President Barack Obama.

The FBI said late Wednesday that it had arrested Paul Kevin Curtis in connection with the letter sent to Obama and another letter sent to Mississippi Senator Roger Wicker.

Authorities said earlier in their investigation that both letters tested positive for the deadly poison ricin.

The U.S. Secret Service said the letter was intercepted at a mail screening facility outside the White House on Tuesday and was immediately quarantined.

Secret Service spokesman Edwin Donovan said the mail screening facility carries out dual inspections for all letters or parcels addressed to the White House. He added that the Secret Service is working closely with the U.S. Capitol Police and the FBI to trace the origins of the letter.