Irene Caselli reports from Caracas: "More marches are expected to take place on Sunday". Photo: BBC NEWS

The demonstrations come at a time of growing political tension in Venezuela.

Three people were killed during anti-government protests on Wednesday, and some 100 students were arrested.

Mr Maduro accused the opposition of stirring up trouble as part of a coup plot and urged his supporters to march for peace on Saturday.

Government supporters began arriving at Venezuela Square, in central Caracas, in the morning.

They were dressed predominantly in red or in Venezuela's national colours - blue, yellow and red.

'Alarming reports'

Hours later Mr Maduro addressed thousands of his supporters in Bolivar Avenue. The march was broadcast live on national television.

"I call all the people to the streets in order to defend peace," he said.

He warned that his government would not give in to those he described as "fascists," including former president of neighbouring Colombia, Alvaro Uribe.

"Alvaro Uribe is behind this, financing and directing these fascist movements.

"He intended to use a Venezuelan television channel [NTN24] to do the same they did on 11 April 2002," Mr Maduro said, referring to a failed military coup against the late President, Hugo Chavez.

Mr Uribe, a centre-right politician, was a fierce enemy of Mr Chavez and accused the late president of supporting Colombia's largest rebel group, the Farc.

Mr Maduro said police had been looking for opposition leader Leopoldo Lopez, accused of ordering "all these violent kids, which he trained, to destroy half of Caracas to then go into hiding".

Mr Lopez has not been seen in public since an arrest warrant was issued for him on Wednesday.

The United States Secretary of State, John Kerry, has issued a statement expressing concern by the rising tensions in Venezuela.

"We are particularly alarmed by reports that the Venezuelan government has arrested or detained scores of anti-government protestors and issued an arrest warrant for opposition leader Leopoldo Lopez," read the statement.

Opposition demonstrators, including a movement known as Mothers in White, gathered at Las Mercedes neighbourhood in eastern Caracas.

Thousands of people, mostly wearing white, marched towards the Courts of Justice building and stopped for a memorial ceremony to the three demonstrators killed on Wednesday: Bassil da Costa, Juan Montoya and Robert Redman.

Student leader Enrique Altimari said the main aim of their "peaceful protest" was to "pay tribute to the victims".

'Not after dark'

He said the march would end before night fell, to avoid a repeat of the incidents of Wednesday.

The three victims were shot dead by unknown gunmen as the opposition marches came to an end.

"The streets at night are not a safe place for us. We would not be achieving any goal and would only fall in the trap set up by violent pro-government groups," Mr Altimari said.

The opposition march ended before dusk with clashes between police, who fired tear gas in attempts to disperse the crowd, and demonstrators who hurled stones.

Reports say three people were injured.

The main opposition grievances are high inflation, crime and the shortage of some staples.

The government has blamed the shortages on "saboteurs" and "profit-hungry corrupt businessmen".

Venezuelan politics has become increasingly polarised.

Mr Maduro was elected last April by a narrow margin, defeating the centre-right candidate, Henrique Capriles, who denounced electoral fraud.

A former union leader, Mr Maduro was a close ally of President Hugo Chavez, who died of cancer last March after 14 years in office.

Mr Capriles says the government's left-wing policies have led to economic collapse, including high inflation - 56.2% in 2013, according to official figures.