(Adds details from the clashes, policeman shot dead)
By Eyanir Chinea and Diego Ore
CARACAS, May 8 (Reuters) - Venezuelan troops on Thursday rounded up hundreds of youth activists and dismantled camps set up to protest against President Nicolas Maduro, and a policeman was shot dead in the demonstrations and clashes that ensued around Caracas.
Pre-dawn raids by National Guard troops broke up four tent camps maintained by student activists in the capital of the OPEC member nation during three months of protests.
After the raids, hundreds of demonstrators and residents poured onto the streets, setting up barricades, a common tactic during three months of unrest. The protests had waned in recent weeks even as sporadic clashes continued.
Masked youths hurled stones and petrol bombs, while police fired tear gas in upmarket east Caracas.
One policeman died of bullet wounds, among five people injured, authorities said. Witnesses said shots were fired from buildings down into the streets.
"A sniper killed the policeman while he was cleaning debris left by these violent, murderous protesters," a somber Maduro said during an address to the nation. "He was vilely killed."
Troops cleared away the remnants of the camps, where students from all over the country had lived in tents, chanting and strumming guitars beneath banners with anti-government slogans, such as "Maduro, assassin."
"These arrests are irresponsible because this is a peaceful protest and we are not trying to topple the government," said Jose Manuel Perez, 22, a student leader. "Mr. President, think about what you're doing. We demand respect for the students."
The government said soldiers arrested 243 people in camps it said were bases for staging violent protests. Officials displayed items taken including mortars and Molotov cocktails.
The detainees included a pregnant woman and "apparently" one foreigner, officials said.
The near-daily protests of February and March, which saw clouds of tear gas and barricades of burning trash and tires, had waned as opposition sympathizers grew less hopeful that Maduro would be pushed from office.
Official figures show 42 have been killed and nearly 800 injured. About 3,000 people have been arrested since February, with Thursday's round-up leaving about 450 people still in detention.
Francia Cacique, 24, a leader of one of the camps, called the raid illegal and denied the students had been plotting subversive activities.
"They've come up with the excuse of drugs and weapons, which is totally false," Cacique told Reuters via cellphone instant message, saying the detained protesters were being held at a Caracas military base. She was not arrested.
"I call on the world to help us and to realize that this is a dictatorship!"
Opposition demonstrators took to the streets in February to demand Maduro's resignation, complaining of soaring prices, chronic product shortages and abuse by security forces.
Maduro has called the protests an effort to overthrow him through public order disruptions that have snarled traffic, preventing some people from obtaining medical treatment.
The 51-year-old president, who replaced his late mentor Hugo Chavez last year, appears secure in power since the protests have not gone far beyond middle-class opposition strongholds and armed forces heads appear to remain firmly behind him.
But he has seen his approval rating fall to its lowest level yet, 37 percent according to local pollster Datanalis. He also faces a tricky job to turn around Venezuela's ailing economy. (Additional reporting by Carlos Rawlins and Jorge Silva in Caracas, Girish Gupta in Medellin; writing by Brian Ellsworth; editing by Andrew Cawthorne)