A company that provides voting services in Venezuela said recent elections for a constituent assembly in that country were rigged.

Smartmatic, which has provided election technology and support services in Venezuela since 2004, said in an Aug. 2 statement that "we know, without any doubt, that the turn out of the recent election for a National Constituent Assembly was manipulated."

The statement cast further doubt on an election that had already been marred by violence and the imprisonment of opposition leaders.

The London-based company said it estimated that there was a difference of at least 1 million votes between the number of people who actually participated and the number announced by authorities.

Government authorities said about 8 million people had voted, according to news reports. Exit polls suggested that number was closer to 4 million, the Financial Times reported.

Venezuelan President Nicolás Maduro called for the elections in an attempt to rewrite the country's constitution. Critics charged that such a move was unconstitutional and would result in further erosion of civil rights.

On July 31, the U.S. imposed sanctions against Maduro, though not against Venezuela's critical natural resources industry.