President-elect Donald Trump says Venezuela's embattled opposition leader must be protected as President Nicolas Maduro takes the oath of office for a third six-year term.

Venezuela opposition leader Maria Corina Machado was detained at a march in Caracas on Thursday in her first public appearance in months and her ally, former presidential candidate Edmundo Gonzalez, demanded she be freed immediately.

Machado was arrested by government security forces Thursday as she left a rally in Caracas on the eve of Maduro's inauguration after a widely discredited election.