In a statement, department spokeswoman Heather Nauert said the US condemns the "political violence" of August 4, which Caracas says was an attempt by the opposition to assassinate Maduro, and urged the Venezuelan leader to respect the rule of law in the probe of the incident.

"The Venezuelan government's response to this incident has been to arbitrarily detain some individuals and a failure to follow due process," she said.

"In addition, there have been violations of parliamentary immunity, which is protected by Venezuela's Constitution. The United States condemns the alleged use of torture to elicit confessions."

Venezuela has arrested 14 people over the attack, including an opposition politician, a general and a colonel.

Maduro has said the blasts that day were from explosives-laden drones sent to assassinate him, though opposition figures accuse Maduro of fabricating the incident to step up repression.

Nauert said the United States supports calls by the international community for an independent expert commission to investigate the incident.

She reiterated the US call "for the immediate release of all those who are arbitrarily detained, including political prisoners."