By Andrew Cawthorne

BARINAS, Venezuela, June 15 (Reuters) - He had just left his office by car and was passing a nearby church when the state security vans swooped in on Wilmer Azuaje.

Put on a military plane hours later on May 3, the 40-year-old regional lawmaker - one of the best-known opposition figures in the rural home state of former Venezuelan President Hugo Chavez - has not been seen since.

"He's disappeared. They kidnapped him. There is complete silence," said his mother, Carmen Cordero, who has been traveling between Barinas state and the capital, Caracas, to seek information on him at the headquarters of national intelligence service Sebin.

There has been no official word on Azuaje's case, and requests to authorities for information went unanswered.

Azuaje is one of more than 3,000 activists, mainly young protesters, rounded up since massive demonstrations began against President Nicolas Maduro and the ruling Socialist Party at the start of April, according to rights groups.

Nearly half of those remain behind bars.

Opponents of Maduro say the 54-year-old successor to Chavez has become a dictator and unleashed repression to intimidate a population fed up with economic hardship and demanding general elections.

Maduro casts the arrests as a legitimate reaction to "armed insurrection" by violent coup-plotters following a U.S. agenda to take control of Venezuela's oil wealth. Government officials view Azuaje as a ringleader in a particularly sensitive region.

A career politician always courting controversy, he backed Chavez in the early years of his 1999-2013 rule. But Azuaje later split with Chavez, who died in office, and accused the president's increasingly wealthy relatives of corruption in Barinas, a poor agricultural state in the Venezuelan "llanos" or plains where Chavez was born in a mud hut.

In 2010, Azuaje was briefly put under house arrest for assaulting a policewoman in a spat over a vehicle.

An avid swimmer and prominent member of the opposition party Justice First, he aspires to run for the Barinas governorship, currently held by a brother of Chavez.

"He's long been a thorn in the side of the government," added Cordero, wearing a white T-shirt bearing the face of her son, before driving to Caracas on another quest to find him.

'TERRORIST OF BARINAS'

Friends and supporters say Azuaje, who also helps run the family restaurant and tourism business, gave energetic encouragement to anti-Maduro demonstrators throughout April.

He was often the only mainstream politician at the scene of protests, broadcasting live via social media, they say.

Officials and government supporters accused Azuaje of fomenting and financing violence, and urged an investigation.

On social media, some dubbed him "the Terrorist of Barinas" and "Captain Criminal," showing photos of him beside alleged gang members, some in masks.

"He's no angel that man, he's behind all of this, so he has to pay," said Maduro supporter Leonardo Gonzalez, 33, wearing a red T-shirt with Chavez's image, in the scruffy state capital, also called Barinas.

The city, in the middle of rural plains, has seen the single worst bout of unrest in 2-1/2 months of often violent protests across Venezuela. Seven people were killed in the city and hundreds of stores looted in one 36-hour spate of clashes on May 22 and 23.

Nearly 70 people have died nationwide.

Azuaje was last seen being bundled onto a National Guard plane in the middle of the night after being arrested and taken to local Sebin headquarters with his assistant the day before.

Friends and relatives yelled his name from the perimeter fence. "Seeing the person you love treated like that is terrible," said his wife, Kelly Garcia, cuddling their two baby girls at her home. "Wilmer's only crime is to dream and work for a better Venezuela."

(Additional reporting by Francisco Aguilar; Editing by Peter Cooney)

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