Security forces check a building after an explosion was heard while Venezuelan President Nicolas Maduro was attending a ceremony.
Two drones loaded with explosives went off near the president's stand, he added.
A senior US State Department official travelling with US Secretary of State Mike Pompeo in Indonesia when asked about the reported attack on Maduro said, "We've heard the reports".
During the incident, Maduro was speaking about Venezuela's economy in an address when audio of the live television coverage was suddenly cut off.
Mr Maduro said several perpetrators had been arrested and initial investigations pointed to Bogota (capital of Colombia), in collusion with his own opposition.
However, other versions of events attributed the fire to an accidentally exploded gas cylinder.
Three hours after the alleged attack Maduro broadcast accusations against the Venezuelan opposition and Colombian president Juan Manuel Santos.More news: Australia, NZ firefighters fly out to battle deadly California wildfires
Oscar Pérez, a rogue elite helicopter pilot, claimed he carried out the helicopter attack and called on Venezuelans to rise up against the government of President Maduro.
Hundreds of thousands of Venezuelans have fled the country, where food and medicine are in very short supply, and where inflation this year could reach as high as 1 million per cent according to the International Monetary Fund.
Earlier on Twitter, the group said it was made up of "patriotic military personnel and civilians loyal to the Venezuelan people who seek to rescue the democracy of a nation under dictatorship".
Maduro often accuses the opposition and the United States of working together to foment a "coup" to topple him.
The national guard was formed in 1937.
He characterized it as an attack aimed at the embattled president, who was recently elected to a new term in office despite a crippling economic and humanitarian crisis.
Rodriguez said Maduro was not injured, but seven national guardsmen were wounded.