National Guard troops have fired tear gas and plastic bullets to disperse students protesting against the official results in Venezuela's disputed presidential election as Nicolas Maduro, the acting president, was formally declared the winner of Sunday's vote.
The students hurled chunks of concrete and stones back at the troops on a highway in Caracas on Monday.
The demonstrators were trying to reach the western part of the capital, where most of the government is headquartered.
Al Jazeera's Chris Arsenault, reporting from the city, said: "Demonstrators are on the streets across the wealthier areas of Caracas waving flags and banging on pots. Many roads are closed across the capital.
"In Altamira square, a centre of the opposition movement, several thousands youths are burning tyres and protesting. The smell of tear gas lingers in the air."
Henrique Capriles, the opposition candidate, had earlier called on electoral authorities to suspend plans to officially proclaim Maduro as the winner of the election.
Repeating his call for a vote recount, Capriles said on Monday that Maduro would be an "illegitimate president" if he was proclaimed president.
Capriles urged Venezuelans to bang their kitchen pans later in the day if the proclamation went forward - a popular Latin American form of protest known as a cacerolazo - to "let the world know our outrage, our anger".
Following his confirmation, Maduro urged his supporters on Monday to demonstrate across the nation on the same days
that the opposition planned further protests.
"I continue calling for peace, and I call the people to combat in peace," Maduro said on state-run television, calling for "mobilisations across the country" on Tuesday and Wednesday.
Arsenault said: "On the political front, both candidates appear to be entrenched in their positions."
The National Electoral Council said late on Sunday that Maduro had won 50.66 percent of the vote compared to 49.07 percent for Capriles - a difference of less than 300,000 ballots - allowing him to carry forward the policies of the late Hugo Chavez.
Venezuela uses electronic voting machines that print a paper ballot as a back-up for any recounts.
"There should be no doubts about the election results," Maduro said addressing a crowd from the Miraflores presidential palace.
"The institutions are functioning. If 7,500,000 Venezuelans said that Nicolas Maduro should be the president of the republic until 2019, this must be respected - the democracy and the power of the majority."
Maduro, however, said he would welcome an audit. "We are calling for respect of the results," he said.
"If they want do an audit they are welcome to do it. They can do whatever audit they want to do. We trust in the Venezuelan electoral system. We welcome an audit."
Capriles said there were attempts to let people vote after polling stations had already closed.
Turnout was 78 per cent, down from just over 80 per cent in the October election that Chavez won by a near 11-point margin.
Maduro inherited Chavez's formidable electoral machinery, which helped the late leader win successive elections in 14 years, with government employees often seen handing campaign pamphlets and attending rallies in groups.
Both candidates had pledged during the campaign to recognise the vote results.
Maduro was widely expected to win the right to complete the new six-year term Chavez won in October, promising to continue oil-funded policies that cut poverty from 50 to 29 percent with popular health, education and food programmes.
Chavez named Maduro, a former bus driver and union activist who rose to foreign minister and vice president, as his political heir in December before undergoing a final round of cancer surgery.
Chavez died on March 5 aged 58.