Venezuelan President Nicolas Maduro said Tuesday that opposition leader Juan Guaido, who has been recognized by nearly 50 countries as acting head of state, should agree to resolve the struggle for power at the polls.

"Let Mister Clown call elections," the leftist president said during a medical school graduation ceremony in Caracas, urging Guaido to change the government "with votes, as is proper."

On Jan. 23, Guaido, the speaker of the opposition-controlled National Assembly, proclaimed himself interim president hours after US Vice President Mike Pence encouraged him to take that step and assured him of Washington's support.

US President Donald Trump quickly recognized Guaido and roughly 50 other countries have followed suit, including Canada, Colombia, Argentina and Brazil, as well as major European powers France, Germany, Spain and the United Kingdom.

Those nations agree with the Venezuelan opposition that Maduro's May 2018 re-election victory was a sham.

"Call elections, Mr. Self-proclaimed, Mr. Clown," Maduro said Tuesday, hours after the National Assembly agreed to undertake a reform of the electoral system with an eye toward convening new elections.

Lawmakers discussed the electoral overhaul after voting unanimously to authorize the entry of humanitarian aid from the United States and other countries that Maduro's government refuses to accept.

Numerous legislators rose to make speeches about what they described as a humanitarian emergency in the oil-rich nation.

The assembly ordered the Venezuelan armed forces and national police to dismantle the barriers blocking the delivery of the aid accumulating in warehouses in the Colombian border city of Cucuta and two other locations.

The request for international assistance came from Guaido and the Maduro administration denounces the aid initiative as a prelude to US military intervention.

Both the United Nations and the International Red Cross have rejected Washington's approach to aid and say they will continue to work with the government in Caracas.

Guaido, 35, has said that he will organize volunteers to bring the aid arriving in Cucuta, the Brazilian border state of Roraima and the island of Curaçao into Venezuela starting Saturday if Maduro does not relent.

Cucuta is linked to the Venezuelan city of San Cristobal by the Tienditas, a modern bridge completed in 2016 that has never been opened to traffic amid ongoing quarrels between Bogota and Caracas over migration, smuggling and cross-border crime.

As the US shipments began to arrive in Cucuta, the Venezuelan army parked large vehicles on their side of Tienditas, which was already bisected by mental fencing.

Late Tuesday, the Maduro government moved to pre-empt any effort to bring in supplies via the Caribbean, imposing a freeze on travel between Venezuela and the neighboring islands of Aruba, Bonaire and Curacao.

The interdiction on travel to and from the islands is part of "Operation Sentinel, activated by the Bolivarian National Armed Forces FANB four months ago throughout Venezuelan territory to preserve sovereignty against possible unauthorized incursions," official news agency AVN reported.

Known collectively as the ABC Islands, Aruba, Bonaire and Curaçao are self-governing territories of the Kingdom of the Netherlands, whose government is among those that have recognized Guaido as Venezuela's legitimate president.

Besides taking an additional step to secure the borders, the Venezuelan military reaffirmed its loyalty to Maduro in the face of Trump's threat that generals and admirals will "lose everything" if they do not switch their allegiance to Guaido.

The military "will remain deployed and alert throughout the borders, as ordered by our commander-in-chief, to avoid any violation of its territorial integrity," the FANB said in a statement.

"The eyes of the entire world are upon you, today, every day, and every day in the future," Trump said Monday in a speech at Florida International University in Miami, addressing his comments to the Venezuelan military.

"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," he said in front of an audience including many Venezuelan expats.

Senior officers who decline to throw their support to Guaido stand to "lose everything," the US president said, before again suggesting the possibility of American military intervention in the oil-rich South American nation.

"We seek a peaceful transition of power, but all options are open," Trump said.

Venezuela's defense minister, Vladimir Padrino, described Trump's speech as an act of "extreme arrogance."

"It is imperative to reiterate to the world that we are witnessing an escalation that has resorted to the hybrid warfare method, to suffocate the economy by imposing an economic and financial blockade, which is aimed at generating ungovernability, chaos and anarchy," Padrino said, reading from a prepared statement.