The pressure continues to increase on Venezuela's election officials after a close election to replace the late president Hugo Chavez.
Opposition leader Henrique Capriles on Monday called on Venezuelans to take to the streets Tuesday after election authorities formally proclaimed Mr. Chavez's chosen successor as the next president.
((OPT SOUNDBITE IN SPANISH -- HENRIQUE CAPRILES:
"I want to say to the government's candidate (Maduro) the loser today is you and say that firmly. You are the loser. You and your government. I say that with firmness and with all the compromise and transparency. We will not recognize the results until each and every Venezuelan vote, one by one, has been counted. We demand here that the National Electoral Council open all of the boxes and that each Venezuelan vote be counted.''
Election official said acting President Nicholas Maduro was elected by a margin of 50.7 percent to 49.1 percent over Capriles -- a difference of a little more than 230,000 votes out of 14.8 million cast.
Capriles' demand for a recount was echoed by the United States and the Organization of American States.
White House spokesman Jay Carney said a recount is necessary and prudent to ensure Venezuelans have confidence in the results.
OAS chief Jose Miguel Insulza has offered to send OAS election experts to help.
Maduro supporters gathered in the streets of Caracas to celebrate the election. The 50-year-old former bus driver and foreign minister told the crowd to "fight" to continue the Chavez legacy.
"Long live Chavez, long live Chavez, long live Chavez. Until victory forever, lets go to the streets to defend this victory, to defend the triumph, in peace and in order to celebrate with the people and to remember that we have complied with the commander. Chavez I promise you, we have fulfilled your inauguration, independence and a socialist fatherland.''
Cuban President Raul Castro was among the first to congratulate Mr. Maduro in a statement published in the Communist Party newspaper Granma.
Mr. Maduro began the campaign with a double-digit lead in the polls over Capriles, a 40-year-old state governor who lost decisively to Mr. Chavez in last year's presidential election.
But Mr. Maduro's lead shrank considerably in the lead-up to Sunday's vote. Capriles accused the Maduro and Chavez governments of doing little to solve Venezuela's economic problems, food shortages and soaring crime rate.
Mr. Maduro has pledged to continue what he calls the Chavez revolution, which supporters say used oil wealth to lift millions out of poverty.
Mr. Chavez died last month after a two-year battle with cancer.
He was a staunch socialist who was first elected president in 1998. He earned the enmity of the United States and others for such policies as nationalizing major companies and courting world leaders like Cuba's Fidel Castro, Iran's Mahmoud Ahmadinejad and Libya's Moammar Gadhafi.
The opposition accused him of becoming a dictator, but he was revered by many of Venezuela's poor.