Mail bombs were delivered to five different businesses in Amsterdam, Rotterdam and Utrecht over the past week, police said on Thursday. Each of the bombs was potentially dangerous, but luckily none of them exploded.

Authorities cautioned the public to be alert for any letters from CIB in Rotterdam. All of the suspicious, bulging letters carried the CIB logo and Wilhelminakade address of debt collection firm Centraal Invorderings Bureau. In each instance, the CIB logo and address were printed on one label, and the recipient's information was printed on a second label.

"The letter bombs did not cause any damage because the explosives did not detonate, but could have caused serious bodily injury," police said. Investigators believe that the same suspect or suspects sent all of the bombs. There were no arrests announced by authorities.

Bij een autodealer aan de Autolettestraat in Rotterdam is een verdacht pakketje aangetroffen. De EOD heeft het pakketje onschadelijk gemaakt en neemt het mee. De Forensische Opsporing doet onderzoek, de winkel is weer open. pic.twitter.com/HxHgXVICVG — MediaTV (@mediatvnl) January 2, 2020

The mail bombs were discovered at a hotel and a gas station in Amsterdam, an automotive business and a gas station in Rotterdam, and a real estate agency in Utrecht. Police in Rotterdam were called to the scene of a suspicious package at the Van Mossel Mercedes Benz on Autolettestraat in Rotterdam on Thursday just before 1:50 p.m.

A sixth bomb was also found at the headquarters of Centraal Invorderings Bureau on Thursday, police said. Detectives ruled out any direct involvement between the debt collection business and the explosives mailed over the past week.

Police said anyone who comes into contact with a letter matching the above description should not open the envelope, and instead should immediately call 1-1-2 to speak with emergency services.