CARACAS: Thousands of opponents of Venezuela’s leftist government marched to jails on Friday demanding the release of opposition leaders they say are political prisoners in the country’s deadly crisis.

It was the latest in a month of demonstrations that have left 28 people dead in clashes between riot police and anti-government protesters, according to prosecutors.

A crowd yelling “Freedom!” rallied near the Ramo Verde prison on the outskirts of Caracas.

That is where the most prominent of the prisoners, Popular Will party leader Leopoldo Lopez, is being held.

It was the latest in a month of volatile and deadly demonstrations.

The centre-right-led opposition is demanding elections to remove President Nicolas Maduro. It blames him for an economic crisis that has caused shortages of food, medicine and other basics.

Lopez was arrested in 2014 and later sentenced to 14 years on charges of inciting violence during deadly riots.

A lead prosecutor in the case later alleged irregularities in his conviction.

Lopez’s wife, Lilian Tintori, has become one of the international faces of Venezuela’s political crisis.

She has travelled to meet with foreign officials to raise awareness of her husband’s fate.

“They did not let us go to see Leopoldo ... We have gone a month without seeing or hearing him,” she told reporters near the prison.

“They say he is being held in isolation as a sanction. Freedom for all political prisoners,” Tintori said.

Groups of opposition supporters walked more than 14 kilometres (nearly nine miles) to the prison from various parts of Caracas.

Others gathered near an intelligence service detention centre in Caracas. Similar marches were called in other cities.

On the road to Ramo Verde, military police mounted a barrier of trucks and metal fencing.

Attempts by protesters to march towards other sensitive state institutions have erupted into deadly violence over recent days.

The United States, European lawmakers and other international authorities have urged Maduro’s government to free people they called political prisoners.

The opposition says there are 170 such detainees.

The government denies they are locked up for political reasons, insisting they were jailed for violent crimes or conspiracy.

A further 1,000 people have been arrested since the latest wave of violence erupted on April 1, authorities say.

Protesters took to the streets in anger at attempts by the courts to strengthen Maduro’s grip on power.

Maduro accuses Washington of leading a plot to overthrow him and says the economic crisis is a US-backed capitalist conspiracy.

On Thursday his government gave formal notice to the Organisation of American States (OAS) that it is launching the process to leave the key diplomatic grouping.

Maduro’s government announced the move on Wednesday, in anger at OAS pressure over the crisis.

He accuses the OAS and its secretary general Luis Almagro of plotting against him along with the United States.

“To the imperialists I say: enough,” he said in a speech late Thursday. “Don’t meddle in Venezuela.”

Venezuela’s interim representative to the OAS, Carmen Luisa Velasquez, handed a letter signed by Maduro to Almagro at a meeting in Washington, confirming the start of the two-year process to leave.

Maduro has refused to hold a general election before the next scheduled one due in late 2018.

“I want to live in a democracy again,” said one demonstrator, retired teacher Reina Romero, 71, told AFP on Friday.

— AFP