Opposition leader Henrique Capriles accused Nicolas Maduro's government on Wednesday of stealing the April 14 presidential election, which he has not conceded the president won.
Political tensions soared as both the government and Capriles called massive street rallies for May 1.
"The truth -- and it is as big as our country is wide -- is that you stole the election. That is the truth. You stole this electoral process, and you have to explain that to this country and to the world," a defiant Capriles said at a news conference.
Capriles demanded that the National Electoral Board begin reviewing the April 14 balloting process and electoral proceedings, in which he had alleged widespread irregularities. He wants a full recount, which the board says is legally impossible.
"We are giving you your deadline: it's tomorrow. We are not going to wait any more," Capriles said in a nationally televised address.
"You (the board) made a commitment to the Venezuelan people; well, I made a commitment to the Venezuelan people too."