Mercosur was set up in March 1991

The 72 members of the assembly will hold their first session on Tuesday, and then will be meeting once a month.

Senior officials from the five members - Argentina, Brazil, Paraguay, Uruguay and Venezuela - attended the event.

Mercosur's secretariat head Carlos Alvarez said their main responsibility would be to boost regional integration.

Mercosur is South America's leading trading bloc. It was set up in 1991.

The 1994 Treaty of Ouro Preto gave the body a wider international status and formalised a customs union.

Known as the Common Market of the South, it aims to bring about the free movement of goods, capital, services and people among its member states.

Bolivia, Chile, Colombia, Ecuador and Peru are associate members. They can join free-trade agreements but remain outside the bloc's customs union.