Yahoo Japan, the Asian country's biggest internet portal, has delayed the launch of its high-speed internet access service by one month.

The company said the delay to the service, called Yahoo BB or broadband, was because it was concerned about its reliability.

"We have received a large number of subscribers and under these conditions we felt that it was necessary to extend the launch date by a month to test the reliability of our services," said Yahoo Japan.

The high-speed service, known as ADSL or asymmetric digital subscriber line, is more than 100 times faster than conventional internet connections.

The service was announced by Yahoo Japan and its parent Softbank in mid-June to take on the existing internet providers such as former state monopoly Nippon Telegraph & Telephone (NTT).

All talk?

Masayoshi Son, Softbank's president, vowed to put the resources of his group of companies behind the service to achieve its target of one million households by the end of December.

But despite the fanfare, Yahoo BB has fallen victim to the same steep cost of building the infrastructure that ended an earlier attempt by Tokyo Metallic to take on NTT.

There have been media reports that Yahoo has connected fewer than 10,000 subscribers instead of the planned 200,000 for the launch.

Tokyo Metallic's fate was sealed when it was taken over by Softbank two days after the announcement of Yahoo BB.

Yahoo and Softbank shares were punished on the Japanese stock market on Monday, with Yahoo losing 1.45% and Softbank plummeting 7.3%.