Internet portal operator Livedoor Co. has cranked up its rivalry with online shopping mall Rakuten Inc. by offering to answer a potential SOS call from Tokyo Broadcasting System Inc.

Livedoor has told TBS it is willing to step in and help if the latter's business-integration talks with Rakuten break down and the broadcaster becomes the target of a hostile takeover bid, company sources said Friday.

But Livedoor, which mounted a hostile bid of its own for Fuji Television Network Inc. earlier this year, will move only when TBS seeks help from a third party, the sources said.