Turnout figures in Venezuela's Constitutional Assembly election were manipulated by least one million votes, Smartmatic, a company which has worked with Venezuela since 2004 on its voting system, said on Wednesday.

"We know, without any doubt, that the turn out of the recent election for a National Constituent Assembly was manipulated," Smartmatic CEO Antonio Mugica said at a news briefing in London.

"We estimate the difference between the actual participation and the one announced by authorities is at least one million votes."