The powerful southern-hemisphere rugby bloc will get another member next year when Argentina turn the Tri-Nations into the Four Nations.

And if further plans are successful, it could even become a southern version of Europe's Six Nations, with the Pacific islands, Asia and even the US joining in.

Greg Peters, the new CEO of Sanzar, which runs rugby in the southern part of the globe, outlined some of these plans in an interview with Reuters this week ahead of the Super 15 launch today.

Having brought rugby union to the heartland of Aussie Rules with the Melbourne Rebels making their Super 15 debut today against the Waratahs, Peters said the next focus would be Argentina.

The Pumas will be brought into next year's international programme in the southern hemisphere and Peters said he had been impressed by what the Argentines were doing to prepare for their debut and that consideration of any further expansion in either competition would have to wait until after that was achieved.

"We have to ... get the Pumas playing and performing competitively, which I've no doubt they will given they came third in the 2007 World Cup," he said.

"They're competitive, particularly at home, and I think they'll give all three of the Sanzar teams (the Boks, Wallabies and All Blacks) a bit of hurry up when they get down to play them in Buenos Aires or wherever in Argentina.

"That'll be really interesting and bring a new dynamic to the tournament and then we'll be considering the future - not only Argentina - there's the Pacific Islands and Asia and perhaps the States to consider as well.

"There are lots of potential opportunities in the future but at the moment we are concentrating on making the current evolution successful."

There are already strong voices from the Pacific calling for greater participation. The prime minister of Tonga, Lord Tu'ivakano, this week criticised the International Rugby Board for preventing the island nation's players from returning to play for their homeland.

Most of the best rugby players from the Pacific islands are lured to New Zealand or Australia as youngsters, but because of IRB rules they cannot return to represent their homelands even after their careers with their adopted countries are over.