A little-known group called the 'National Movement of Soldiers in T-shirts' claimed responsibility for the attack.

US National Security Advisor John Bolton told Fox News in an interview on Sunday that the United States was not responsible for the blast, suggesting that the Maduro government itself could have instigated the attack.

"It could be a lot of things from a pretext set up by the Maduro regime itself to something else," Bolton said.

Opposition critics often dismiss such incidents as fabrications meant to distract from hyperinflation and Soviet-style product shortages, and say Maduro frequently exaggerates security threats for political gain.

The OPEC nation is struggling under the collapse of a once-prosperous socialist system, with millions now struggling to eat or find medicine – causing a growing exodus of citizens.

Maduro, who blames the country's problems on an "economic war" led by adversaries, during the course of his five-year rule has often announced having foiled military plots against him that he says are backed by Washington.

"They tried to kill me today, and I have no doubt that everything points to the Right, the Venezuelan ultra-Right," Maduro said in a broadcast after the incident, referring to the opposition.

"Maximum punishment! And there will be no forgiveness."

Bolivar Avenue of downtown Caracas, where the incident took place, was calm on Sunday morning. Joggers and cyclists were taking up two of the lanes that are traditionally used for weekend recreation. The stage where Maduro spoke had been removed.

Reuters