Protesters in Fresh Clashes with Venezuelan Police

Dozens of hardcore protesters in Caracas threw rocks and lobbed firebombs at riot police who retaliated with tear gas Monday, after Venezuela's opposition upped the ante on President Nicolas Maduro.

At least three people were detained in the clashes in a middle-class district of the capital, on the eve of the one-month anniversary since the start of nationwide protests, said the director of the non-governmental Venezuelan Penal Forum, Alfredo Romero.

At least 18 people have died and more than 260 have been injured in escalating demonstrations that started on February 4, the government says.

Earlier in the day, Venezuela's opposition called for new protests against Maduro amid a week of holidays and commemorations of late socialist leader Hugo Chavez's death.

"We're going to gather to pay homage to all those who have fallen as a result of the brutal repression of this dictatorial regime," said Corina Machado, second-in-command of the Popular Will party, outlining plans to hit the streets again on Tuesday.

The Popular Will's leader Leopoldo Lopez is being held by authorities, among more than 1,000 people rounded up in demonstrations against soaring inflation, fast-rising crime and the clampdown on protests that have roiled Caracas and other major cities almost daily.

Machado led a march of some 2,000 people to the Organization of American States, urging the continental body to get involved.

Meanwhile, two-time opposition presidential candidate Henrique Capriles called for another demonstration on Saturday to denounce the country's chronic food shortages.

Writing on Twitter, Capriles urged his supporters to join "a great national mobilization against SHORTAGES which affect the majority of people!"

Maduro says the protests are a US-backed plot by "fascist" elements to overthrow him. He blames high prices and food shortages on speculators and hoarders, meanwhile the government is putting the final touches on ceremonies to mark the one-year anniversary of Chavez's death on Wednesday.

The commemoration follows an extended Carnival holiday after Maduro added two days to the long weekend in what the opposition saw as a bid to stop its momentum.

Despite that, tens of thousands of people flooded the streets of Caracas and other cities on Sunday.

The government's official television network has been showing images of beachgoers and Carnival dancers.