Three Venezuelan air force generals accused of plotting a coup against the leftist government of President Nicolas Maduro were arrested Tuesday, amid a widening crackdown on the opposition.

The unidentified generals were in contact with opposition politicians and "were trying to get the Air Force to rise up against the legitimately elected government," Maduro told a meeting of South American foreign ministers.

"This group that was captured has direct links with sectors of the opposition and they were saying that this week was the decisive week," Maduro said.

The stunning disclosure -- the first known significant threat from within Maduro's government -- comes amid a growing crackdown on the president's opponents after more than six weeks of street protests that have left at least 34 dead.

In a further blow to the opposition, the mayor of the town of San Cristobal where the protests started was sentenced to a year in prison. Daniel Ceballos was convicted of failing to prevent violence and the blockading of streets.

He was the second mayor convicted and sentenced, and quickly. Enzo Scarano, mayor of San Diego in the north, was arrested, tried and sentenced to 10 months in prison. It all happened in a matter of hours last week.

An opposition leader, Leopoldo Lopez, has been detained since last month and is awaiting trial. He is accused of instigating violence against the government.

- Betrayed by loyalists -

The generals have been summoned before a court martial, Maduro said, adding that the plot was uncovered because other officers come forward to say they were being recruited.

Asked for details about the generals, a senior source told AFP that the information is "being handled only through Maduro's office."

It is the first time in 15 years of socialist government that generals have been arrested for alleged coup plotting, said military expert Fernando Falcon, a retired lieutenant colonel.

Massive protests in April 2002 resulted in Maduro's predecessor, the late Hugo Chavez, being briefly ousted -- before he was restored to power for another decade.

Maduro and his government have been the target of near-daily protests fueled by public anger over soaring crime, hyperinflation and shortages of such basic goods as toilet paper.

Demonstrators are also angry at oil-rich Venezuela's close financial and political ties to Cuba, the only Communist one-party state in the Americas.

Maduro earlier had said he fended off a coup bid aided or supported by the United States and other "fascists."

Protests have mainly taken place in middle-class opposition strongholds. Maduro still enjoys support among Venezuela's larger, poor population, allowing him to weather the weeks-long protests.

- Machado defies Maduro -

On Monday, National Assembly president Diosdado Cabello announced that a prominent opposition deputy, Maria Corina Machado, had lost her seat and parliamentary immunity, and could be arrested at any time.

At a news conference in Lima, Peru, a defiant Machado said she would return to Caracas on Wednesday, adding she feared she would be arrested on her arrival.

She said she was returning "because I am a Venezuelan deputy and I will enter Venezuela as such to continue fighting in the streets without rest until we achieve democracy and freedom."

Machado angered the government by going before the Organization of American States last week as a guest of Panama to discuss the crisis in Venezuela.

Panama's representative to the OAS, Arturo Vallarino, said the move to take away Machado's seat was "proof of the arbitrary acts being committed in Venezuela."

Last week, two opposition mayors were arrested, and another prominent opposition leader has been in jailed for a month, accused of inciting violence.