The FBI is investigating at least 11 physical attacks on high-capacity Internet cables in California's San Francisco Bay Area dating back a year, including one early Tuesday morning.

Agents confirm the latest attack disrupted Internet service for businesses and residential customers in and around Sacramento, the state's capital.

FBI agents declined to specify how significantly the attack affected customers, citing the ongoing investigation. In Tuesday's attack, someone broke into an underground vault and cut three fiber-optic cables belonging to Colorado-based service providers Level 3 and Zayo.

The attacks date back to at least July 6, 2014, said FBI Special Agent Greg Wuthrich.

"When it affects multiple companies and cities, it does become disturbing," Wuthrich said. "We definitely need the public's assistance."

The pattern of attacks raises serious questions about the glaring vulnerability of critical Internet infrastructure, said JJ Thompson, CEO of Rook Security, a security consulting and services provider in Indianapolis.