President Obama warns Venezuela not to block 'legitimate' drive to recall Nicolas Maduro

US President Barack Obama issued a stern warning to Venezuela's government today to not block the Opposition's "legitimate" efforts to hold a referendum to recall the country's embattled President Nicolas Maduro.

"The democratic process should be respected," Obama said at a North American summit as he stood alongside Canadian Prime Minister Justin Trudeau and Mexican President Enrique Pena Nieto.

"And that includes legitimate efforts to pursue a recall referendum consistent with Venezuelan law," Obama added.

Venezuela is undergoing deep political conflict that has raised tensions in the volatile South American nation as it struggles with an economic crisis.

Obama described the situation as "very serious," and signalled that he, Trudeau and Pena Nieto were united in their position on Caracas.

"Together we're calling on the government and Opposition to engage in meaningful dialogue and urge the Venezuelan government to respect the rule of law and the authority of the National Assembly," Obama said.

He also added that "political prisoners should be released".

Venezuela's Opposition blames Maduro for a deep economic crisis that has caused widespread food shortages and deadly looting.

The Opposition has launched efforts to remove the leader since they took control of the Assembly in January. But Maduro has challenged them through the Supreme Court, which his rivals say he controls.