Brasilia  - The representatives of 12 South American countries met Friday in Brasilia to launch the region's latest integration mechanism, the Union of South American Nations (Unasur), born with the challenge of overcoming current tensions.

Former Ecuadorian president Rodrigo Borja (1988-1992) caused a stir late Thursday when he said that he would not accept the position of Unasur executive secretary.

Marco Aurelio Garcia, a senior foreign affairs advisor for Brazilian President Juiz Inacio Lula da Silva noted Friday, however, that the decision does not weaken the alliance.

"There was no exit because there had been no entry. President Borja had a very ambitious vision, and if it is ambitious it is hard for it to be understood by all members," said Garcia.

He added that Brazil declined to press for approval Friday of Lula's proposal to create a South American Defence Council.

"That will be debated in the second semestre (of 2008)," he stressed.

The project clashed with the opposition of Colombian President Alvaro Uribe, among others.

Analysts note that current tensions in South America are the main challenge for Unasur.

The meeting that was taking place Friday was originally scheduled to be held in March in Colombia, but had to be postponed in the light of the Colombian cross-border raid on Ecuadorian territory on March 1, which killed Raul Reyes second in command of the leftist Revolutionary Armed Forces of Colombia (FARC) and 26 other people.

The incident sparked a severe crisis between Colombia, Ecuador and Venezuela that has only been partially overcome since although Uribe promised never again to carry out raids beyond his country's borders.

In an effort to contribute to overcoming the crisis, Lula was set to meet Friday with Uribe and also with presidents Hugo Chavez, of Venezuela, and Rafael Correa of Ecuador. (dpa)