Riot police with helmets and shields used pepper gas several times to control the crowd as hundreds of pensioners jostled against security lines to attempt a march from a Caracas square.

"Respect the elderly you sons of bitches!" shouted one bearded man, throwing a punch at an officer on the front line.

Since launching protests against Maduro in early April, Venezuela's opposition has sought to vary tactics by staging silent and candle-lit marches, for instance, and rallies for women, musicians and medics.

Each time, the ruling Socialist Party has tried to match them. On Friday, it organized its own rival old people's march next to the Miraflores presidential palace.

At least 39 people have died in the unrest since April, including protesters, government sympathizers, bystanders, and security forces. Hundreds have also been hurt and arrested.

Decrying Maduro as a dictator who has wrecked the OPEC nation's economy, opponents are seeking elections, foreign humanitarian aid, freedom for hundreds of jailed activists, and autonomy for the opposition-controlled legislature.

Maduro, a 54-year-old former bus driver and successor of Hugo Chavez, says his foes are seeking a coup with the support of the United States and encouragement of international media.

Chanting "Freedom!" and "Down with Maduro!", the elderly protesters made it onto a highway but were blocked from their intended destination, the state ombudsman's office, by police with armored vehicles. A representative of the office listened briefly to their grievances on the street instead.

The crowd, including plenty of octogenarians plus a nun and one white-haired man dressed as Santa, sang Venezuela's national anthem in front of the security cordon. Opposition leaders joined them, hugging and linking arms with the pensioners.

'MORE TEAR GAS THAN FOOD'

Venezuela's elderly have been hard hit by four years of brutal recession, leading to shortages of food and medicines, long lines at shops and runaway prices.

"Each tear gas cannister costs more than the minimum (monthly) salary, the government spends more on tear gas than providing food," complained university professor Francisco Viveros, 67.

"I'm here for the youth, the students, those who are going onto the streets. We've lived our lives so we should be at the front."

There were also old people's protests in western Tachira and southern Bolivar states, with those demonstrations able to reach the local headquarters of the ombudsman.

Scores of government supporters also gathered in Caracas near Miraflores palace, wearing red, punching their fists in the air and chanting pro-Maduro slogans. "The opposition are killers," said Nelia De Lopez, 65, with a tattoo of Chavez on her arm.

Long viewed by many poor Venezuelans as an out-of-touch elite, the opposition now enjoys majority support.

It thrashed the government in 2015 parliamentary elections, but was blocked from holding a referendum on Maduro last year and suffered another blow when 2016 state elections postponed.

Opposition leaders want the 2018 presidential vote brought forward, but there is no sign of that happening and Maduro is creating a controversial "constituent assembly" with authority to rewrite the constitution and shake up public powers.

"The opposition doesn't understand the constituent assembly, but it does know about death, assassination and terrorism," Socialist Party No. 2 Diosdado Cabello told a rally in east Monagas state, condemning violence by opposition supporters.

While the opposition believes it has more momentum than at any other time during Maduro's four-year presidency, officials appear to be banking on protesters tiring in the streets and are also hoping for rise in oil prices to ease the economic crisis.