ATLANTA (CNN) - Users of Sprint's mobile and landline long-distance phone service in the western United States faced a widespread outage Monday after a fiber-optic cable was cut in California, the phone company said.

The outage affected customers using long-distance and Internet services across much of the region, and it was not clear Monday evening when services would be restored.

The problems began about 3:30 p.m. ET and affected wireless phones on the Sprint PCS and the Nextel networks, as well as landline service, said John Taylor, Sprint's manager of public affairs. Internet service on Sprint Nextel phones is also being delayed, the company said.

Sprint (Research) crews were working on some emergency maintenance near Reno Junction, Calif., on the California-Nevada border, when the outage occurred.

"At approximately 3:30 p.m. eastern time, a fiber optic cable was cut between Phoenix and Palm Springs, California," said Taylor. "We believe it was a third party cut, not a Sprint crew, but we can't confirm yet who was responsible," he said.

Taylor said Sprint and Nextel customers had no problems making or receiving local calls, and he was not aware of any disruptions to 911 service or other local emergency calls. He did not have any estimates on the number of customers affected.

Sprint, based in the Kansas City suburb of Overland Park, Kan., is the fourth-largest U.S. phone company. The company already had rerouted network traffic through Phoenix when the cut occurred, making the outage more widespread than it would have been, Taylor said.

When a fiber optic line is cut, the repair can be a tedious process, requiring scores of lines to be spliced together. As of 6:30 p.m. ET, Sprint crews were beginning to repair the accidental cut in the Phoenix area.

"We apologize to our customers for the inconvenience, our crews are working as fast as possible to restore service," Taylor said.