Bomb threat letters were sent to post offices in Robbinsdale and Anoka on Friday, and the incidents appear to be connected.

Both post offices were closed for at least an hour. A bomb-sniffing dog from the Minnesota State Patrol found nothing suspicious at the Robbinsdale post office, said Capt. Jim Franzen. He said the letter was vague and didn’t give a specific date or time for the threat.

He said the letters appeared to be sent by the same person. He didn’t know if anything was found at the Anoka post office.

Anoka police referred media calls to the local U.S. Postal Inspection Service office, which didn’t return a reporter’s call.