Donald Trump says Venezuela's embattled opposition leader must be protected, as President Nicolas Maduro prepares to take the oath again after allegedly stealing an election.

Venezuelan President Nicolás Maduro was sworn in Friday to a third term despite credible evidence that his opponent won the latest election and following protests in the South American country and abroad against his increasingly repressive rule.

Venezuela's President Nicolas Maduro, whose nearly 12 years in office have been marked by a deep economic and social crisis, was sworn in for his third term on Friday, remaining in power despite a six-month-long dispute over a contested July election and international calls for him to stand aside.