SEOUL, Aug 1 (Reuters) - A furious dispute with Japan over who owns a desolate cluster of rocks has turned into a marketing opportunity for South Korean business tapping into patriotic fervour.

One bank has set up a popular "cyber branch" in the tiny Dokdo islands -- called Takeshima in Japanese -- which lie about halfway across the sea to Japan.

Mobile phone companies have joined in.

Some have ringtones based on a song eulogising South Korean rule over the islands. And one is offering a "Dokdo is our territory" call plan that lets subscribers donate to a campaign to promote the islands internationally as South Korean territory.

And clothing companies are busy pushing a range of T-shirts on the theme, with slogans such as "I love Dokdo."

One daily showed a photograph of an official handing out badges to travellers at the country's main international airport with the slogan :"Dokdo is Korean territory!!".

The latest furore erupted in July after Japan, Korea's colonial ruler from 1910-45, advised schools to teach that the islands were Japanese.

Both countries say their claims go back centuries though the diplomatic squabble has looked more intense after it was realised that the cluster of rocks might sit above valuable gas deposits.

Local media reported that some of the products on sale are leftover stock from the last patriotic flurry over the islands in 2005.

"It's natural that companies are grabbing the chance to take advantage ... when the patriotic sentiment is at its peak," said Kim Rando, a consumer studies professor at Seoul National University.

"But this marketing strategy that appeals only to patriotism could give rise to excessive nationalism," he added. (Reporting by Kim Junghyun; Writing by Jonathan Thatcher)

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