Venezuela's opposition on Thursday kept pressure on beleaguered President Nicolas Maduro after protests demanding his ouster amid a mounting political and economic crisis.

The opposition-controlled congress held a session to lambaste the leftwing leader, who has introduced a state of emergency he warned could be bolstered if "violent" acts against his government occurred.

The opposition has rejected the decree and called on the army to swap sides to be "with the constitution."

Henrique Capriles, a top opposition leader, tweeted that Maduro "is considered void and nobody should respect him."

On Wednesday, around 1,000 protesters tried to march in Caracas to demand electoral authorities respect a petition for a recall referendum against Maduro, one of two dozen opposition rallies across the country.

But they were blocked by hundreds of riot police, some of whom fired tear gas. A few demonstrators threw rocks and bottles.

Maduro's United Socialist Party said seven police officers were hurt in the capital. Thirty people were arrested in the various protests across the country, according to the opposition and rights groups.

The confrontations exacerbated international concern over oil-dependent Venezuela, whose economy is being torn apart by a brutal recession, hyperinflation and food and electric power shortages.

- US 'deeply troubled' -

Former Spanish prime minister Jose Luis Rodriguez Zapatero was in Caracas trying to mediate some sort of detente between Maduro and the opposition.

On Wednesday, the head of the Organization of American States, Luis Almagro, said Maduro would be considered yet another "petty dictator" if he continued to reject the referendum.

The US State Department said it was "deeply troubled" by the situation in Venezuela. A spokesman said: "Reports of excessive use of force and violence against protesters obviously is troubling to us and of deep concern."

Senior US intelligence officials have already said they believe the South American nation is in "meltdown" and at risk from public revolt.

A senior Vatican official, Paul Richard Gallagher, secretary for relations with states, canceled plans to visit Venezuela next week amid the escalating unrest.

Maduro has heaped blame for the tide of adversity on the "imperialist" United States, which he accuses of conspiring with Venezuela's "fascist" right to overthrow him.

To counter foreign "armed intervention" Maduro has ordered military exercises for Saturday.

The defense minister, General Vladimir Padrino Lopez, on Thursday said the drill, termed "Independence 2016," would show off military planning sparked when US President Barack Obama last year designated Venezuela a threat to US national security.

Padrino Lopez, speaking in a televised address, said the exercise would be "unprecedented" in scope and rely also on Venezuelan civilians, but gave no details of what it would entail.

The accusation of US meddling is the same as Maduro's late predecessor, Hugo Chavez, often raised.

But it appears Maduro has not convinced Venezuela's population, 70 percent of which wants a new government, according to recent polls.

"The people no longer want revolution," said Migdalia Lopez, 51, lining up for bread in the town of Guarenas, east of the capital.

"What they want is food."

- Disputed petition -

The president has vowed that the opposition referendum will never take place.

"I will not hesitate" to ratchet up the state of emergency "to fight for the peace and security of this country" if necessary, Maduro said Wednesday.

His extraordinary measures came into effect this week for a period of 60 days. They can be renewed and Maduro has said they probably will be, through next year.

His order gives sweeping powers to the security forces to impose public order, and to help distribute food.

Even though the congress has rejected the decree, the Supreme Court, which is stacked with Maduro loyalists, is likely to confirm it.

In that case, the opposition has called for the public to defy the state of emergency.

It has also accused the National Electoral Council (CNE) of stalling on validating the petition, which it said attracted 1.8 million signatures.

Maduro and his vice president, Aristobulo Isturiz, claim the petition is riddled with fake signatures and there is no basis for a referendum.

Instead, Istruriz has urged the opposition to sit back and contest the next presidential election due in December 2018.

"If you win, Maduro will give up power. Easy. What's the problem?" he asked.

If the opposition manages to bring about a recall referendum, the vote must constitutionally be held before January 10, 2017 for it to trigger new elections.

Any later than that, a successful recall vote would simply transfer power from Maduro to Isturiz.