At least four 7-Eleven stores in the San Fernando Valley were robbed at gunpoint Friday morning and police were working to determine if the robberies were connected.

The first robbery was reported at a store in Van Nuys about 12:45 a.m., followed 30 minutes later by a robbery at a store in Northridge and additional robberies occurred at stores in Chatsworth and Granada Hills, according to the Los Angeles Police Department.

It was unclear how much money was taken in each incident, police said.