Authorities are investigating a white powdery substance that was delivered in greeting cards to three locations Monday in the Merrimack Valley, said State Fire Marshal Stephen D. Coan.

“Our regional hazmat team for that area of the state has ­responded to three locations, in Methuen, Lawrence, and ­Haverhill,” said Coan. “Each one of them has some similarity. Each recipient received a greeting card through the US mail today with a return ­address in Haverhill that contained an unidentified white powdery substance.”