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 Nicolas Maduro, whose nearly 12 years in office have been marked by a deep economic and social crisis, is set to be sworn in for a third term on Friday, staying in power despite a six-month dispute over a July election and international calls for him to stand aside.

Venezuelan President Nicolás Maduro will be sworn in for a third six-year term after a reelection widely viewed as illegitimate and as his administration grows increasingly brazen in cracking down on its opponents.