At least four people have been killed, including a police officer, after thousands of Venezuelans opposing President Nicolas Maduro took to the streets of Caracas following two weeks of anti-government protests across the country.

Gunfire erupted in the centre of the capital when armed members of a pro-government vigilante group arrived on motorcycles and began firing at more than 100 anti-Maduro student protesters clashing with security forces, the AP news agency reported.



As the crowd fled in panic, one demonstrator fell to the ground with a bullet wound in his head. Onlookers screamed "assassins"' as they rushed the 24-year-old student, later identified by family members as Bazil D'Acosta, to a police vehicle.



Also killed was the leader of a pro-government 23rd of January collective, as supporters of Venezuela's government call themselves.



National Assembly President Diosdado Cabello said the "revolutionary'" known by his nickname Juancho was ``vilely assassinated by the fascists" but provided no further details.

Luisa Ortega, the country's attorney general, said a police officer had died during the violence and that 25 peole had been injured.

The mayor of the Chacao's District in eastern Caracas said a fourth person had also been confirmed dead.



'Single culprit'

Wednesday's protest, organised by students and hardline opposition members, was the biggest faced by Maduro since he was elected nearly a year ago following the death of his mentor, Hugo Chavez.

Pro-government supporters countered with a march of their own to express support for Maduro, who has accused opponents of trying to violently oust him from power just two months after his party's candidates prevailed by a landslide in mayoral elections.

While anti-government demonstrators vented frustration over issues ranging from rampant crime to mounting economic hardships, they were united in their resolve to force Maduro out of office by constitutional means.

"All of these problems - shortages, inflation, insecurity, the lack of opportunities - have a single culprit: the government," Leopoldo Lopez, a Harvard University-trained former mayor, told a crowd of about 10,000 people gathered at Plaza Venezuela in Caracas.

Lopez, who leads a faction of the opposition that has challenged what it considers the meek leadership of two-time presidential candidate Henrique Capriles, called the protests "a moral and patriotic duty".

"If we don't do it now, then when? And if it's not us, who will?"

'Nazi faction'

Across town, Maduro told his supporters that he would not back down in the face of what he said was a conspiracy by opponents to provoke violence and destabilise his government.

"A Nazi-fascist faction has emerged that wants to take Venezuela down the path of violence," the 51-year-old former bus driver said. "What we're going to have is peace and prosperity."

Protests also took place on Wednesday in other cities, including Merida and San Cristobal, where students have clashed with police in recent days.

Merida's Mayor Carlos Garcia told the AP news agency that three people were injured by gunfire in protests on Tuesday after a group of hooded government supporters began firing into the crowd.

Maduro on Wednesday acknowledged the incident, but told supporters that those responding to the opposition's violent provocations were not true revolutionaries.

Human rights groups on Tuesday denounced a government crackdown on peaceful protests, which has led to the arrest of 13 anti-government activists in the past two weeks on "anti-terrorism" charges.