By Diego Oré

CARACAS (Reuters) - Venezuelan supermarkets are increasingly being targeted by looters as swollen lines and prolonged food shortages spark frustration in the OPEC nation struggling with an economic crisis.

Shoppers routinely spend hours in lines to buy consumer staples ranging from corn flour to laundry soap, turning lines into venues for shoving matches and now more frequent attempts to plunder shops.

The economic crisis has hit President Nicolas Maduro's approval ratings and raised tension levels in the country.

Fifty-six incidents of looting and 76 looting attempts took place in the first half of 2015, according local NGO Venezuelan Observatory of Social Conflict, which based the figures on media reports and testimony of observers around the country.

On Sunday, a small crowd in the western city of San Cristobal pushed its way into the government-run Bicentenario supermarket to grab products after it had closed, leaving staff scratched and bruised, according to store manager Edward Perez.

"As we were closing, a group of 20 people unexpectedly started shouting insults at the government and the workers," said Perez in a telephone interview.

Several looters were arrested after the fracas, which Perez blamed on "ultra-right-wing sectors of the opposition" seeking to sow violence.

Last Friday, one man was killed and 60 were arrested in Ciudad Guayana in southern Venezuela after shops were looted.

The government did not respond to a request for comment on the lootings but Maduro calls the shortages and the unrest a product of an opposition-led "economic war".

More frequent than these serious events are minor melees that ensue when delivery trucks arrive at stores carrying prized products such as chicken or milk.

But the combination of limited official information and exaggerated rumors propagated via Twitter often makes it difficult to distinguish between the two.

KNIFED IN LINE

Lines have been noticeably longer since the start of the year, and have been especially tense since last Friday's incident in Ciudad Guayana.

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"There's no organization, they treat you like an animal, they don't respect anything," said Carmen Neskowi, 49, who identified her profession as "standing in line," in a queue outside a Caracas supermarket. "It's an insult."

The problems, however, have not spurred a broader wave of protests like those led by the opposition in early 2014 that left 43 people dead.

Supporters of the ruling Socialist Party note that the network of subsidized state-run grocery stores created by late president Hugo Chavez and financed by plentiful oil revenue helped reduce poverty and hunger during his 1999-2013 rule.

But the combination of dysfunctional currency controls, which have limited Venezuela's capacity to import, and the end of a decade-long oil boom has left Maduro's government strapped for cash and struggling to maintain the largesse.

According to polls, his party is expected to do poorly in legislative elections later this year, its support hit by high inflation, the currency's collapse and food shortages.

Local food producers ranging from neighborhood bakeries to an industrial pasta maker have halted or slowed operations for lack of raw materials or machine parts.

Obtaining low-cost food and medicine, once the hallmark of the Chavez era, has become a daily struggle.

Lines are increasingly filled with smugglers who buy subsidized goods and resell them at a profit on the black market or in neighboring Colombia, generating tension between resellers and those trying to stock their own kitchens.

Josefa Bracho, a 70-year-old teacher in the central city of Barquisimeto, vows not to stand in any more supermarket lines. She was slashed in the thigh with a scalpel after a dispute in a line with women she believed were smugglers.

"We'd been in line for almost four hours when three women got in front of me," said Bracho in a telephone interview.

"I said 'What are you doing? Why are you cutting in line?' Later one came by and cut my leg ... Standing in line means putting my life in danger."

(Additional reporting by Liamar Ramos and Corina Pons, Writing by Brian Ellsworth; Editing by Kieran Murray)