(AP) President Hugo Chavez blamed President Bush for a growing election boycott in Venezuela Thursday, hours after all the country's major opposition parties joined the ballot protest.

Thousands of Chavez supporters massed in the streets to protest the pullout, with some calling it a desperate measure by parties that have lost political support.

"I denounce it before the world and hold responsible for this new conspiracy against Venezuela the very chief of the empire, Mister Danger, the president of the United States," Chavez said during a speech.

"We will defeat the electoral coup," Chavez said, adding without giving specifics.

The move by the entire opposition in joining the boycott, cleared the way for candidates aligned with Chavez to expand their dominance of congress in a vote this weekend.

Pro-Chavez candidates are aiming to win a two-thirds majority in the 167-seat National Assembly in Sunday's polls, which would allow them to rewrite portions of the constitution and push back term limits for the presidency and other offices. Currently, pro-Chavez lawmakers hold 52 percent of the legislature.

Opposition parties, which have trailed in recent polls, accuse the electoral council of a pro-Chavez bias and expressed concerns a computerized voting system could compromise confidentiality.