from Sunday's election after results showed a narrow victory for late President Hugo Chavez's hand-picked successor, Nicolas Maduro.
The election authority has ruled out a recount, raising fears of more violence in the South American nation, which has the world's largest oil reserves. The country saw waves of street protests during various parts of Chavez's tumultuous 14-year socialist rule.
The deaths happened on Monday when hundreds of protesters took to the streets in various parts of the capital Caracas and other cities, blocking streets, burning tires and fighting with security forces in some cases. Officials also said 135 people were arrested in the post-election violence.
State media and officials said the fatalities included two people shot by opposition sympathizers while celebrating Maduro's victory in a middle-class area of Caracas.
One person died in an attack on a government-run clinic in a central state. Two, including a policeman, were killed in an Andean border state, officials said.
"We will defeat this violent fascism with democracy," said foreign minister Elias Jaua, describing incidents and showing video footage to a group of ambassadors.
"Those who attempt to take with force what they could not acquire through elections are not democrats."
There was no immediate response from the opposition, and Capriles' camp reiterated demands for peaceful protests on Tuesday as thousands of his supporters marched to regional election offices around the country.
The government held counter-demonstrations.
After Sunday's vote, Capriles refused to recognize the results, and his followers poured into the streets. In Caracas on Monday night opposition supporters banged pots and pans, and Maduro backers responded with fireworks and music.
In a wealthy district of Caracas, police fired tear gas and rubber bullets in a battle running into Monday evening with masked, rock-wielding opposition supporters. Motorcyclists drove in circles around a pile of burning trash along the capital's principal highway.
Capriles said his team's figures show he won the election and he wants a full recount. The National Electoral Council said an audit of 54 percent of the voting stations, in a widely respected electronic vote system, had already been carried out.
The election was triggered by the death of Chavez last month after a two-year battle with cancer. He named Maduro as his successor before he died and his protege won the election with 50.8% of the vote against Capriles' 49.0%.
"Where are the opposition politicians who believe in democracy?" Maduro said, blaming Capriles for the violence.
Capriles, the governor of Miranda state, hopes to highlight the weakness of Maduro's mandate and stir up opposition anger over his charge that the electoral council is biased in favor of the ruling Socialist Party.
The strategy could backfire if demonstrations turn into prolonged disturbances, such as those the opposition led between 2002 and 2004, which sometimes blocked roads for days with trash and burning tires and annoyed many Venezuelans.
A return to protracted trouble in the streets could renew questions about the opposition's democratic credentials on the heels of their best showing in a presidential election, and just as Capriles has consolidated himself as its leader.
LEGAL MOVE AGAINST CAPRILES?
Senior government figures have raised the possibility of legal action against Capriles.
"Fascist Capriles, I will personally ensure you pay for the damage you are doing to our fatherland and people," National Assembly head Diosdado Cabello said on Twitter, saying he would seek a criminal investigation by state prosecutors.
But the Opposition leader said he will fight on.
"We are not going to ignore the will of the people. We believe we won ... we want this problem resolved peacefully," Capriles told a news conference.
"There is no majority here, there are two halves."
Opposition sources said their count showed Capriles won by more than 300,000 votes.
His team said it has evidence of some 3,200 election day irregularities, from voters using fake IDs to intimidation of volunteers at polling centers. It sought an exhaustive check of the paper-ballots printed at the time of casting a vote.
The focus of Monday's protests in the capital was the Plaza Altamira, which was often site of opposition demonstrations during Chavez's polarizing 14-year rule. Burned-out debris and glass lay strews on the ground on Tuesday morning.
"We will protest for as long as it takes. We will not give up the streets," said Carlos Cusumano, a 20-year-old student who took part in the protest.
Wearing T-shirts wrapped around their faces, some demonstrators threw sticks and stones at the ranks of police, who wore body armor and carried shields.
Maduro, who had initially said he was open to a recount, called on his supporters to demonstrate all week. The official results showed him winning by 265,000 votes.
"Maduro won and the people have proclaimed him," said dental technician Alicia Rodriguez, 38. "Learn to lose!" she added in reference to the opposition's stance.
The controversy over Venezuela's first presidential election without Chavez on the ballot in two decades raised doubts about the future of "Chavismo" - the late president's self-proclaimed socialist movement - without its towering and mercurial founder.
Chavez named Maduro as his heir in an emotional last public speech to the nation before his death, giving the former foreign minister and vice president a huge boost ahead of the vote.
Maduro's margin of victory raises the possibility he could face future challenges from rivals in the leftist coalition that united around Chavez, who won four presidential elections.
At his last election in October, the former soldier beat Capriles by 11 percentage points even though his battle against cancer had severely restricted his ability to campaign.