Verizon Wireless was scrambling on Wednesday to resolve an outage of its highest-speed U.S. wireless network, on which the top U.S. cellular carrier is relying to drive future growth.

The venture of Verizon Communications and Vodafone announced on its Twitter feed that its newest network -- based on Long Term Evolution, a high-speed data technology -- suffered an outage that held up data-transfer flows on some devices.

The operator said that while voice calls were working on the Thunderbolt, an HTC Corp <2498.TW> device that is Verizon's first LTE-enabled phone, data speeds on that phone may slow.

It also said that customers were temporarily unable to activate any LTE devices.

After alerting customers to the problem on Wednesday morning, Verizon said by late afternoon that it had discovered the cause and was working with vendors to restore connections.

The company did not say when the network would return to normal but it expected to fix the problem on a market-by-market basis.

Verizon Wireless is banking on so-called LTE for its next phase of growth in wireless, with most of the U.S. population already owning cellphones. It kicked off LTE services in some markets late in 2010 and is now expanding the network.

Competition is intensifying in the world's second-largest telecommunications market by users, with AT&T Inc now in the process of buying Deutsche Telekom's T-Mobile for $39 billion -- creating the industry leader and leapfrogging Verizon in the United States.

(Reporting by Sinead Carew; Additional reporting by Helen Kearney; Editing by Gary Hill)

Verizon Communications Inc. Broadband