Venezuelan security forces fired tear gas and made several arrests as 20,000 people marched on Saturday in the capital Caracas against what they see as President Nicolas Maduro's heavy-handed repression of dissent.

At least 31 people have been killed in more than six weeks of student-led protests against the government, representing the biggest challenge yet to Maduro, the elected socialist heir to longtime late president Hugo Chavez.

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

Demonstrators partly blame Caracas's close ties to Cuba, the only Communist one-party state in the Americas.

Saturday's colorful rally in Caracas was peaceful until a group of masked youths attempted to block a busy highway, triggering a brief intervention from riot police and security forces who fired tear gas and water cannon to disperse them.

The youths responded by throwing stones and more tear gas was fired to prevent protesters blocking streets. At least six people were arrested, AFP journalists said.

There were also demonstrations in other cities such as Valencia, in the north, and Merida and San Cristobal in the west.

"In the name of freedom, put an end to dictatorship now," read one of the many banners held aloft in the Caracas protest, where opposition leader Henrique Capriles led one of several rallies.

Maduro, who succeeded leftist leader Chavez last year, has combined calls for dialogue with a hard stance against opposition rivals and demonstrators.

Maduro says he has 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 and Maduro still enjoys support among Venezuela's larger, poor population, allowing him to weather the weeks-long protests.

The crackdown on opposition figures contrasts with Maduro's call for rivals to join a "peace conference."

The main opposition refuses to join the dialogue until the government frees more than 100 protesters who remain behind bars.