WELLINGTON (AFP) - Southern Hemisphere rugby chiefs will soon discuss including teams from Japan and Argentina in an expanded Super 15 competition, reports said.

New Zealand Rugby Union (NZRU) chief Steve Tew has confirmed that the Sanzar countries - South Africa, New Zealand and Australia - want to expand the tournament when the current broadcast deal expires at the end of 2015, New Zealand Newswire reported.

It said he was reluctant to discuss details, but options reportedly include adding teams from Argentina or Japan to enlarged New Zealand and Australian conferences.

"If we are going to expand then there's probably room for expansion in more territories than just Argentina," Tew said.

Sanzar chief executive Greg Peters hopes to finalise a blueprint for the proposed revamp before the end of this year so it can be pitched to broadcasters, the New Zealand Herald reported.

"We will know the format we are working towards (by year's end) but these things occasionally have something unravel as they go along," he said.

Changes to the competition are required to meet South Africa's insistence that it field six teams, rather than the current five entered by all three countries.

Tew said the NZRU had a number of non-negotiable conditions for the new format, including that it is not longer than the current version, that travel is kept to a minimum and that quality is not diluted.