Letters with 'suspicious substances' sent to US senators and 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.

Coming just weeks before the US midterm elections, it echoes previous security scares involving suspicious mail.

The suspicious letters were sent to at least five Democratic senators' offices, most of which were intercepted before delivery.

They include California's Alex Padilla, Connecticut's Chris Murphy and New York's Kirsten Gillibrand, the senators' offices confirmed to the BBC.

New York Senator Chuck Schumer and Delaware Senator Lisa Blunt Rochester were also sent the suspicious pieces of mail, according to the BBC's US partner CBS News.

"This incident is a stark reminder of the very real danger facing those who serve the public and who help administer our elections in the face of increasingly hostile political rhetoric," Padilla said in a statement to the BBC.

Delaware's Department of Elections said its office received and opened a letter containing a white powdery substance on Thursday, adding that staff followed security protocols on handling suspicious mail.

The Oklahoma State Election Board and the Louisiana secretary of state both said this week that their offices had received letters containing a white powder.

The Louisiana office was evacuated after a staff member opened the package on Tuesday, but it has since reopened after law enforcement found no evidence of harmful substances.

Ohio Secretary of State Frank LaRose said his office was the intended recipient of a letter containing white powder, but the USPIS had intercepted it.

The New York State Capitol in Albany and the Wyoming State Capitol in Cheyenne also received suspicious packages, according to emergency responder scanner feed reviewed by the BBC.

"This FBI and the US Postal Inspection Service will continue to safeguard the public and secure elections for American citizens," the agencies said in a statement on Thursday.