The FBI is investigating the latest incident in a string of physical attacks on fiber optic cables that has left part of California without Internet access.

Three cables, housed in an underground vault, were found slashed on Tuesday morning, USA Today reports. It is the 11th time in the past year that Internet cables in California have been sabotaged. All of the incidents have occurred between Sacramento and the Bay Area. 

The attacks have all been at facilities that "unmonitored" by security devices, such as cameras, Business Insider points out. Authorities believe It's not a coincidence that the proximity of locations are in the same region.

"When it affects multiple companies and cities, it does become disturbing," FBI Special Agent Greg Wuthrich told USA Today. "We definitely need the public's assistance."

JJ Thompson, CEO of Rook Security, told USA Today that the attacks may be occurring to test security response times.

"When it's situations that are scattered all in one geography, that raises the possibility that they are testing out capabilities, response times and impact," Thompson said. "That is a security person's nightmare."

The FBI has not been able to figure out the motive behind what is happening, but Business Insider's Nathan McAlone notes that the many tech companies, in San Francisco specifically, don't have the best reputation among consumers.

"The relationship between the tech sector and the general population has been fraught with tension over the past few years in San Francisco," McAlone writes. "Protesters have accused companies like Google of callously driving residents out of the area, and destroying the unique culture of the Bay Area."