Masked youths are once again blocking streets and burning tires in the Venezuelan city of San Cristobal, the epicenter of last year's massive anti-government protests.

The groups are small and the unrest contained, but dissent is rising in this volatile Andean city, a barometer of frustration with nationwide shortages that are putting pressure on the socialist government of Nicolas Maduro.

Students, who also accuse the government of corruption and repression but whom Maduro labels "coupsters," are threatening to unleash larger demonstrations again.

"It's time," Deiby Jaimes, 21, said from behind a barricade of burning trash as police gazed down from their hilltop perch. "There's a social, economic and political crisis. Economically we're completely lost and in a delirium."

But Jaimes and other students said they were restraining themselves to see if other Venezuelans also take to the streets.

Last year's protests split the opposition and failed to attract widespread support from Venezuela's poor, meaning mainstream anti-government leaders like Henrique Capriles are calling for less radical tactics including peaceful rallies and a good showing at an upcoming parliamentary vote.

"People are scared," said Jaimes, an accounting student, as dozens around him knocked rocks together menacingly. "But fear is disappearing due to shortages. We're expecting a social explosion."

More here: Venezuela's 'Protest City' on Edge as Economic Crisis Deepens