US President Donald Trump on Monday urged Venezuela's military to accept opposition leader Juan Guaido's amnesty offer, or stand to "lose everything," as a crisis deepened over President Nicolas Maduro's refusal to let in desperately needed humanitarian aid.

Bringing in humanitarian aid is crucial to the viability of Guaido, who has denounced Maduro's re-election last year as fraudulent and in January declared himself interim president, a move recognised by some 50 countries.

He has given the Maduro government until Saturday to let shipments of mainly US aid into the country.

Addressing supporters and Venezuelan expatriates in Miami, Trump said he had a message for officials helping keep Maduro in place.

"The eyes of the entire world are upon you today, every day and every day in the future.

"You cannot hide from the choice that now confronts you. You can choose to accept president Guaido's generous offer of amnesty to live your life in peace with your families and your countrymen.

"Or you can choose the second path: continuing to support Maduro. If you choose this path, you will find no safe harbor, no easy exit and no way out. You will lose everything."