Venezuela crisis drags on

• Maduro thanks military for preventing coup
• Opposition leader Guaido calls for mass protests
• Blackout causes havoc, kills 15 kidney patients

Venezuela's opposition leader Juan Guaido on Saturday called for a nationwide march on Caracas to crank up the pressure on embattled President Nicolas Maduro, as the country endured its third night largely without power.

The massive blackout crippling the oil-rich but economically troubled South American nation has fuelled the political standoff between Guaido, who is recognised as Venezuela's leader by more than 50 countries, and Maduro, who is clinging to power.

No national data was available about the impact of the power outage, but an NGO said at least 15 patients with advanced kidney disease died after they stopped receiving dialysis treatments in darkened hospitals.

As night fell Saturday, the power across much of the country -- which first went off Thursday -- was still not on. Businesses remained shut, hospitals struggled to operate, and public transport barely functioned.

The 35-year-old Guaido, the head of Venezuela's National Assembly, earlier told thousands of supporters that he would soon embark on a nationwide listening tour before leading a march on the capital.

"Once we've finished the tour, the organization in every state, we'll announce the date when all together, we'll come to Caracas," Guaido said, a megaphone in his hand as he stood on the roof of a pickup truck.

Security forces had prevented the opposition from setting up a stage at their original protest site, arresting three people.

Guaido threatened to authorise an outside military intervention "when the time comes," pointing to the constitution, which authorizes "the use of a Venezuelan military mission abroad, or foreigners inside the country."

"All the options are on the table," he said, borrowing a phrase from US President Donald Trump.

Maduro also rallied his supporters. Wearing red, they protested against "imperialism" at a march that marked four years since the United States branded Venezuela a "threat" to its security and imposed sanctions.

Maduro referred to Guaidó as "a clown and a puppet" of the US. "They invited the armed forces to carry out a military coup and their reply was clear - they have defeated the coup plotters," he said.

Maduro also said almost 70 percent of power had been restored by mid-day.

Both the pro-Guaido and the pro-Maduro rallies ended without major incident.