Its 500-plus-members, who include Mr. Maduro’s wife and son, are led by Delcy Rodriguez, Mr. Maduro’s former foreign minister.

A controversial new Venezuelan assembly packed with allies of unpopular President Nicolas Maduro held its first session on August 4, 2017, deepening a rift with the opposition and in the teeth of international criticism from the U.S., the E.U. and major Latin American nations calling it illegitimate.

The Constituent Assembly has supreme powers over all branches of government as it takes on its principal task of rewriting the 1999 constitution. It was elected last weekend in balloting marred by violence and allegations of fraud.

Its 500-plus-members, who include Mr. Maduro’s wife and son, are led by Delcy Rodriguez, Mr. Maduro’s former foreign minister.

They took their seats in an ornate oval chamber under a golden dome in the 145-year-old Legislative Palace — in the same building where the opposition-dominated National Assembly is located, albeit in a different room.

"Today is a magnificent day," Mr. Rodriguez, 48, said to applause. "I want to thank Maduro for having stirred the wise powers of the Venezuelan people."

She rejected what she called "foreign interference" in the new assembly's creation.

The Constituent Assembly has discretion to dissolve the National Assembly. Such a move, however, would fuel criticism of it as a rubber-stamp body for Mr. Maduro, who critics say is building a "dictatorship".

The assembly's members were accompanied to the palace by Mr. Maduro and thousands of supporters carrying portraits of late president Hugo Chavez.

"The people today are going back to the assembly building and will never leave," said one supporter, 72-year-old Euclides Vivas.

The opposition staged protests in the capital on August 4, 2017, but there were no signs of the street violence of the past four months that has left a death toll of more than 125.