Cuban President Fidel Castro has joined Venezuelan President Hugo Chavez and other Latin American leaders at a Mercosur economic summit in Cordoba, Argentina. During Friday's meeting, Venezuela formally entered the trade bloc and the group signed a trade agreement with Cuba.

Argentine President Nestor Kirchner, the host of the summit, called on the trade bloc to make greater strides in fighting poverty, discrimination and unemployment.

He also welcomed the group's newest member, Venezuela, calling the entry of the oil producing nation historic.

President Castro, who turns 80 next month, made a surprise trip to Argentina for the summit. He and Venezuela's President Chavez are outspoken critics of the United States.

President Chavez also travels on to countries that are to include Belarus and Iran, two nations which have been at odds with the United States.

At the summit Friday, Mercosur leaders signed a trade pact with Cuba, the communist island that has been under an economic embargo by the United States for more than four decades.

Ian Vásquez of the CATO Institute, a policy research group in Washington, says some nations in Latin America are missing a great economic opportunity by not seeking expanded trade with the United States. "There is a move in parts of Latin America, not all of Latin America, that likes to emphasize trade regionally, rather than with the United States, that is throughout the hemisphere, as a better solution, and this I think has been a tremendous mistake."

He also expressed concern about the membership of Venezuela in Mercosur. "Venezuela adamantly is opposed to free trade, and especially to free trade with the United States. As a member of Mercosur, it (Venezuela) will have an influence on the policies that Mercosur follows, so I don't think that is a benefit, even if it does expand the market somewhat beyond the current Mercosur members," he said.

The Mercosur trade group was formed in 1991 by Argentina, Brazil, Paraguay and Uruguay. Chile and Bolivia are associate members.