Rugby's Tri-Nations will become the Four Nations in 2012 with the last hurdle cleared for a full-strength Argentina to enter the annual competition.

The Pumas' brute force, which propelled them to third at the 2007 World Cup, will challenge the Wallabies, All Blacks and Springboks after the International Rugby Board ensured they would have access to their best players.

A participation agreement is yet to be signed with governing body SANZAR but the path was Thursday cleared with the IRB approving a player availability regulation forcing European club sides to release Argentinian players for Four Nations internationals.

"Today's announcement represents an historic milestone in the process of Argentina's integration into an expanded Tri Nations tournament and is an extremely exciting development," said IRB chairman Bernard Lapasset.

The expanded Four Nations will be played from mid-August to October, during the start of the Northern Hemisphere season where the large majority of Pumas ply their trade.

Previously, Argentina - ranked No.6 in world rugby, ahead of England, Wales and Scotland - had been seen as a potential addition to Europe's Six Nations tournament due to their club commitments.

But, as part of the integration, Pumas stars will be assisted in joining Super 15 teams from next year.

More are expected to gravitate towards South African franchises but there are sure to be Australian Rugby Union discussions to open up opportunities Down Under.

While the fledgling Melbourne Rebels can sign up to 10 foreign players, the ARU's current foreign-player policy restricts the Reds, Waratahs, Brumbies and Western Force to just two imports.

Wallabies flanker and NSW skipper Phil Waugh on Thursday endorsed the addition of the hard-nosed Pumas to an eight-week Four Nations where each team played the others on a home and away basis.

"The Argentinians are a strong side," he said. "They showed that in the World Cup and obviously a lot of their players play in a strong comp in the French and European competitions.

"And it's not a bad place to go either so I think the guys are looking forward to perhaps playing them over there."

The IRB's latest move comes after the body in March agreed to match the contribution of SANZAR by paying $2.5 million annually from 2012-15 to help Argentina compete in the tournament.

"It will add a dynamic new element to the current Tri Nations, which is already regarded as one of the worlds toughest tournaments," said SANZAR chief Steve Tew.

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