TIME-WARNER-FOX/

A routine maintenance by Time Warner Cable resulted in a nationwide internet outage for hours on Wednesday in the U.S.. The company, which is being acquired by rival cable company Comcast, has about 11 million high-speed internet subscribers. (Brendan McDermid/REUTERS)

Time Warner Cable says routine maintenance of its internet service caused a nationwide outage that started early this morning and is still affecting some customers.

The company says it is investigating the cause of the problem, which occurred with its internet backbone, the paths that local or regional networks connect to in order to carry data long distances.

The company says the problem affected all of its markets and started at 4:30 a.m. local time, and was largely restored by 6 a.m., with updates continuing to bring all customers back online.

The outage sparked widespread complaints on social networks.

Time Warner Cable, which operates in about 30 states and is being acquired by rival cable company Comcast, has about 11 million high-speed internet subscribers.