The service starts with coverage of the Democratic National Convention

The service, ABC News Now, starts on Monday with non-stop coverage of the Democratic National Convention.

ABC News president David Westin said he was "eager to find out" how many viewers it would attract.

"We wouldn't be doing this if we didn't suspect there was a business for us in the long run," he added.

ABC owns 10 television stations across the US, with a total of 3.5 million digital cable subscribers.

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The network is currently trying to persuade its 64 affiliated stations that broadcast on digital cable television, to provide ABC News Now to a further 18.5 million homes.

It will also be available to subscribers with broadband internet access at a cost of $4.95 (�2.69) every month.

Some internet service providers, including America Online, will include it in current subscriber packages for no extra cost.

In addition, some Sprint PCS Vision mobile phone customers will also be able to see ABC News Now for $9.95 (�5.41) a month.

The network will not sell advertising for ABC News Now - but its affiliates, who are being encouraged to place their own regional news, weather and sports bulletins on the channel, would be free to do so, Mr Westin said.