Argentina has taken a major step joining an expanded Tri-Nations rugby competition in 2012 after the IRB changed player availability rules, rugby officials said yesterday.

The current Tri-Nations participants - New Zealand, Australia and South Africa - said the final step will be negotiating a participation agreement with Argentina.

The three nations, who organise the Tri-Nations and Super 14 competitions through their SANZAR joint venture, said Argentina would add a dynamic new element to what will become the Four Nations series.

"This is an exciting step for SANZAR and for world rugby, as it confirms Argentina's participation in a top-flight rugby competition," said SANZAR and New Zealand Rugby Union chief executive, Steve Tew.

"We now need to finalise a participation agreement with (the Argentinian union) so we can move to full planning for the introduction of Argentina in 2012," he said.

Under the IRB availability rule change, clubs will have to release players for the competition to be played from late August to early October each year.

SANZAR also said it will try to provide more opportunities for Argentinian players to play in the Super rugby competition in the lead up to the Four Nations series.