(Adds details from security operation)
By Esteban Israel and Deisy Buitrago
CARACAS, March 16 (Reuters) - Venezuelan troops stormed a Caracas square on Sunday to evict protesters who turned it into a stronghold during six weeks of demonstrations against President Nicolas Maduro.
National Guard soldiers fired tear gas and turned water cannons on hundreds of demonstrators who hurled rocks and some petrol bombs before abandoning Plaza Altamira, in affluent east Caracas, which has been the scene of daily clashes.
Some soldiers rode into the square on motorbikes, rounding up a dozen demonstrators, Reuters witnesses saw. One flashed a "V" for victory as he was driven away, another shouted "Help!"
The troops then began demolishing protesters' barricades, apparently carrying out Maduro's vow to retake the square.
"We are going to carry on liberating spaces taken by the protesters," the 51-year-old successor to late leader Hugo Chavez said in a speech at a pro-government rally in a different part of Caracas on Sunday.
Militant opposition leaders and students have been urging Venezuelans onto the streets to protest issues ranging from crime and shortages of goods to the presence of Cuban advisers in Venezuela's army and other state institutions.
Earlier on Sunday, thousands marched towards the Carlota military air base in the latest daily demonstration against the socialist government. The protests began in early February.
"I spend five or six hours in a queue just to buy two packets of flour, or two bottles of cooking oil," said pensioner Pedro Perez, 64, in the opposition rally.
"Also, I'm protesting over insecurity and the lies this government tells Venezuelans, bringing Cuban soldiers here ... This is an ungovernable country, we can't carry on like this."
In another day of rallies around the nation, thousands of government supporters also marched peacefully in Caracas to praise the government's food welfare policies.
"We are going to strengthen the brotherhood between the Venezuelan and Cuban peoples," Maduro told that rally in response to the opposition march's anti-Cuba slogans.
Venezuela supplies more than 100,000 barrels per day of oil to Cuba, for which it is partly paid by the presence of more than 30,000 medics, sports trainers and others from the Communist-ruled Caribbean island.
Outside Caracas, opposition party Popular Will said that members of the armed forces had stopped and beaten several politicians trying to visit imprisoned protest leader Leopoldo Lopez at the Ramo Verde jail about an hour from the capital.
Lopez, who heads the Popular Will party, was arrested last month on charges of fomenting violence.
In a handwritten interview with pro-opposition newspaper El Universal, Lopez, 42, said he had developed a strict regime of exercise, studies and writing from his prison cell.
"I try to be disciplined because I'm aware that in jail, the main tools of my struggle are my mind and spirit," he said.
Despite the turbulence in Caracas and other cities around Venezuela, Maduro seems in little danger of being toppled by a "Venezuelan Spring."
The armed forces seem firmly behind him, the numbers of protesters are far fewer than a wave of demonstrations against former president Chavez a decade ago, and opposition leaders are divided over the wisdom of street tactics.
However, Maduro has come under pressure from some foreign governments and rights groups over excessive use of force from his security forces. Some 21 officers have been arrested for brutality allegations.
A prominent local pollster and analyst, Luis Vicente Leon, said on Sunday that both the government and the opposition's approval ratings had suffered from the recent troubles.
"Many people have asked 'who's winning?' My answer is: 'no one,'" Leon wrote in a local newspaper, saying the social and economic crisis had hit Maduro's popularity while the opposition's credibility was also suffering.
Leon referred to data that he said proved that, but did not give numbers. Most pollsters are preferring to keep findings private at the moment due to the tense political situation. (Additional reporting by Andrew Cawthorne in Caracas; Writing by Andrew Cawthorne; editing by Matthew Lewis)