AT&T has increased its reward to $250,000 for information leading to the arrest and conviction of those responsible for cutting fiber-optics lines at four locations early Thursday morning in South San Jose and San Carlos.

The sabotage led to widespread disruption of phone service — including land lands, some cell service, Internet access and 911 emergency service — in southern Santa Clara County as well as in Santa Cruz and San Benito counties. Service was completely restored by the wee hours Friday morning.

“We have zero tolerance for any criminal who would attack our network and harm customers,” AT&T spokesman John Britton said. “We’re going to aggressively work with law enforcement to see those responsible are apprehended and prosecuted to the fullest extent of the law.”

Police today are continuing their investigation into who deliberately cut fiber-optic cables in two underground locations in San Jose and two more in San Carlos around 1:30 a.m. Thursday in an apparent coordinated act of sabotage. The FBI is helping with the investigation.

Crews in South San Jose spent Thursday fusing four separate cable lines back together, some working eight feet deep in a manhole at Monterey Highway and Blossom Hill Road and others working with the pulled slack above ground, a few feet from a sign that said in red letters, “Warning: Buried Fiber Optic Cable in This Vicinity. Call Before You Dig.” Nearby, authorities later discovered more cut cable lines at Hayes Avenue and Cottle Road, ﻿which affected several hundred customers in the Hellyer, Silver Creek Valley and Tures neighborhoods.

Cables were also severed at two locations in San Carlos, but no disruption of service was detected. Authorities believe all four incidents are related.

AT&T, whose cable lines leased to Verizon were cut, initially offered a $100,000 reward for information leading to the arrest and conviction of those responsible. Britton said that amount was the largest reward in his 17 years with the company.

Mercury News Staff Writers Julia Prodis Sulek, Ken McLaughlin and Mike Swift contributed to this report. Contact Mark Gomez at mgomez@mercurynews.com or (408) 920-5869.