CARACAS, Venezuela -- Thousands of Venezuelans mourned the passing of President Hugo Chavez on the first anniversary of his death Wednesday, while National Guard troops fired tear gas and rubber bullets at anti-government activists who pressed on with street protests despite the commemorations.

Chavez's successor, President Nicolas Maduro, angrily announced that he would break off relations with Panama, which he accused of being a "lackey" of the U.S. in a conspiracy to topple his government through the daily protests that have left at least 18 dead since mid-February.

Maduro said he made the move because Panama asked for the Organization of American States to study the situation in Venezuela. Maduro considers the OAS to be dominated by Washington.

"We don't accept the interventionism of anyone, because our international policy is a policy of peace, of co-operation, of respect, of the anti-imperialist Latin American union," Maduro said.

Venezuela is mired in economic crisis and daily anti-government demonstrations, and Wednesday was no exception as protests erupted in at least six cities.

"The National Guard attacked with a lot of fury against the guys and used tractors to violently take down the barricades," said Mari Marcano, a protester on the tourist island of Margarita. "They launched a lot of tear gas, shot rubber bullets."

In restive central Lara state, the leader of a small centre-left opposition party, Hector Alzaul Planchart, was shot dead by unknown assailants as he left his party offices in Barquisimeto, according to media reports.

Despite the protests, for many Wednesday's pomp-soaked anniversary of Chavez's passing was a time for sadness and nostalgia. Thousands gathered at the capital's parade grounds to honour the socialist leader who died of cancer on March 5, 2013.

"This isn't like an anniversary; it's like we're mourning," said Gledis Hernandez, 43, who took her daughter and niece to the memorial parade in Caracas. She said Chavez gave her an apartment when her home was washed away in floods, but "right now we're living in a sad situation."

Vendors hawked Chavez T-shirts, pins and hats. Visitors were given a newspaper upon entering the area with the headline "Chavez lives!" on the front and a cardboard cutout of Chavez riding a bike tucked within. Inside, tanks and soldiers paraded before a waving Maduro and military jets screamed overhead.

The military parade, attended by Chavez friends Bolivian President Evo Morales, Nicaraguan President Daniel Ortega and Cuban President Raul Castro among others, kicked off a 10-day commemoration. Afterward, they participated in a ceremony at Chavez's hilltop mausoleum, and that was followed by the television premier of Oliver Stone's documentary "My Friend Hugo."

Maduro seems in a stalemate with the political opposition. His administration shows no sign of crumbling, but he appears unable to stop the student-led protests. Instead, he moves ahead with a peace effort that the opposition calls farcical while his foreign minister rebuffs offers for outside mediation.

Inflation in Venezuela hit 56 per cent last year, slashing the buying power of the poor who Chavez lifted above the poverty line using the state's oil profits. Simple grocery shopping has become a daily odyssey as residents hunt for scarce items like flour, cooking oil and toilet paper, and wait hours in line when they're lucky enough to find them.

Luisa Teresa Guzman, 64, said she still cries over Chavez. Wearing a red beret, red shirt and red pants at the entrance to the parade grounds, she said Maduro can carry the revolution forward. "That's why Chavez left him there."

But a month of protests has drawn international attention to the country's struggles.

"I'm fighting for my country," said Maria Cortez, a 63-year-old community organizer. Dangling from a street sign high above the intersection in a middle-class Caracas neighbourhood was a life-size dummy dressed in surgical scrubs, face mask and booties with a sign that called for Cuban doctors to leave Venezuela. "It's been 15 years of keeping our mouths shut, 15 years and the people can't take it anymore."

In San Antonio de los Altos, in Miranda state, protesters blocked roads, but were driven off by hundreds of National Guard troops, national police and other authorities with tear gas and rubber bullets. At least two were injured, one with a bullet wound in the leg and the other with multiple plastic buckshot wounds to the face, said Lyndons Guzman, emergency director in the Carrizal municipality.

Protests were also reported in Valencia, San Cristobal, Merida and Barinas.

Ruben Velasquez, 44, making his way from the parade grounds, said the protests are simply an expression of the situation people are living now in Venezuela.

He said life had worsened in every way since Chavez's death, particularly with regard to the economy and crime. He supports Maduro, because he works in the government customs agency, but only to a point.

"If things escape from his (Maduro) hands I don't think he's going to have support from anyone," Velasquez said.