At least two people died and at least 17 were injured as anti-government demonstrators in Venezuela clashed with soldiers in the capital Caracas.
The street battles Friday coincided with the opening of the G15 summit of developing nations in Caracas.
Opposition leaders called the march to highlight their demands for a referendum on recalling Venezuela's leftist president, Hugo Chavez.
Demonstrators pelted soldiers with stones and other objects after the troops kept them from reaching the summit venue.
Opposition leaders accuse election officials of using a technicality to delay a decision on the whether the referendum can take place.
Officials have ordered additional, time-consuming checks of some of the petition signatures calling for the referendum to determine whether they are valid. The move has angered opposition leaders, but President Chavez says the petition drive itself is fraudulent.
At the summit, President Chavez did not mention the street clashes in his opening remarks. Instead, he spoke on development issues, saying industrialized countries exert excessive influence on developing nations.
Those in attendance included the leaders of Brazil, Argentina, Iran, Zimbabwe and Jamaica.