Letters with 'suspicious substances' sent to US election offices

• Federal authorities say they are investigating "potentially hazardous" letters containing "suspicious substances" that have been sent to congressional and state election offices around the US.
• The FBI and the US Postal Inspection Service (USPIS) said they were trying to trace the "suspicious mailings", some of which were intercepted before they were received.
• Authorities declined to say how many offices had been targeted, but several secretaries of state and congressional offices reported receiving the letters.