President Nicolas Maduro has accused an international software firm of being part of a US campaign to stain the results of Venezuela's vote for an all-powerful constitutional assembly.
Revelations that turnout figures were apparently manipulated in the vote cast a deeper shadow over the controversial body shortly before it was to convene.
The official count of voters in Sunday's election was off by at least one million, according to the head of the technology firm Smartmatic, a finding certain to sow further discord over a body that has been granted vast authority to rewrite Venezuela's constitution.
Results recorded by Smartmatic's systems and those reported by Venezuela's National Electoral Council show "without any doubt" the official turnout figure of more than eight million voters was tampered with, chief executive Antonio Mugica told reporters in London.
The international software company has provided voting technology in Venezuela since 2004.
Mr Mugica said there was a one million vote discrepancy, but he did not specify whether his company's figures showed one million fewer, or one million more, people participated in the election.
He said: "Even in moments of deep political conflict and division we have been satisfied with the voting process and the count has been completely accurate.
"It is, therefore, with the deepest regret that we have to report that the turnout figures on Sunday, 30 July, for the constituent assembly in Venezuela were tampered with."
Tibisay Lucena, the head of the National Electoral Council, dismissed Smartmatic's claim, calling it an "opinion" of a company that played only a secondary role in the election and had no access to complete data.
"A company located outside the country does not guarantee the transparency and credibility of the Venezuelan electoral system," she said.
Mr Maduro later accused Smartmatic of bowing to US pressure to "stain" the election results.
Standing behind the electoral council's voter count, he proclaimed that an additional two million Venezuelans would have cast ballots if they had not been stopped by roadblocks erected by the socialist government's opponents.
"Nothing and no-one can stop the victory of the people," he said to applause from 500 members of the new assembly.
The president also announced the assembly's installation was being delayed by a day, convening on Friday instead of Thursday in order to "organise it well in peace and tranquillity".
Smartmatic's claim drew an immediate reaction from opposition leaders who have contended since Sunday's results were announced that the National Electoral Council inflated the turnout count.
The opposition - a sizeable portion of the population - boycotted the vote, and an independent exit poll concluded that less than half the government's figure cast ballots.
Opposition leaders said counts from observers stationed in each municipality also suggested the government's numbers were inflated.
Smartmatic, which supplies services worldwide, was founded by Venezuelans in Caracas and began providing voting technology during the presidency of the late Hugo Chavez, who installed the nation's current socialist government.
In the past, opposition members have questioned the validity of results, but the firm has maintained its impartiality.
Mr Maduro called the vote in May after weeks of protests fed by anger at his government over food shortages, triple-digit inflation and high crime.
He has argued the body will help end the violence and protests that have left at least 125 dead, while also vowing to use the system to target enemies and solidify Venezuela as a socialist state.