The head of the air force dismissed him as a traitor, while Mr Guaidó said he expected other military officers to follow suit.
The US and around 20 other countries have recognised Mr Guaidó as Venezuela’s legitimate leader, while Russia, China, Turkey and Cuba have leapt to Mr Maduro’s defence, blasting the move as an old-style US-orchestrated coup.
The EU is torn on whether to embrace Mr Guaidó or not. Member states were due to spell out their positions early on Monday (AEDT) in what has escalated into a geopolitical conflict which could have major implications for Latin America.
“This has been building for a while,” said 28-year-old Alejandro Rosas, an anti-government protester, as he joined a march that snaked through the streets of the capital. “We need a new Venezuela. We’re ready and thirsty for change.”
Across town, a smaller but sizeable crowd of red-shirted government supporters marked the 20th anniversary of the day when Mr Maduro’s predecessor Hugo Chávez took power, launching a socialist revolution that rippled through Latin America, changing the region’s relationship with Washington.
“Reflect!” Mr Maduro urged his opponents. “And if you have a little bit of conscience left, abandon the path of Yankee interventionism, stop supporting a coup that’s already failed.”
Mr Maduro offered to bring forward congressional elections, a move the opposition dismisses as a ruse to give the government control of the one democratically elected institution left in the country — the National Assembly. Mr Guaidó says he wants new presidential elections instead.
He told his supporters humanitarian aid would soon be flown into the country from neighbouring Colombia and Brazil to help millions of Venezuelans suffering shortages of food and medicine.
The US has backed the plan but the International Committee of the Red Cross has reportedly warned Washington of the dangers of such an operation, which would probably enrage the Maduro regime.
The need for aid is pressing. Half of Venezuela’s households live in poverty and over 90 per cent of people say their monthly wage does not cover their basic living costs.
Since Mr Maduro came to power in 2013, the economy has halved in size — a larger contraction in percentage terms than that suffered by the US during the Great Depression. Inflation is running at 1.7m per cent and all-important oil production is at its lowest level since the 1940s.
The US announced tough sanctions against Venezuelan state oil company PDVSA last week in a bid to cut off revenue to the Maduro government, and barred US entities from trading in PDVSA bonds in the secondary market. On Friday, it went a step further and extended the ban to include Venezuelan sovereign bonds too.
Additional reporting by Vanessa Silva in Caracas