Venezuelan opposition leader Juan Guaido declared himself interim president in a defiant speech Wednesday before masses of anti-government demonstrators who took to the streets to demand President Nicolas Maduro's removal.

The bold challenge to Maduro's rule immediately drew recognition from the Trump administration, which called on Maduro to resign and said it would use the "full weight" of U.S. economic and diplomatic power to push for the restoration of Venezuela's democracy. Canada as well as Brazil, Colombia and several other Latin American nations followed suit in throwing their support behind Guaido.

Raising his right hand in union with tens of thousands of supporters, Guaido, the fresh-faced head of the opposition-controlled congress, took a symbolic oath to assume executive powers he says are his right under Venezuela's constitution and to take over as interim president until he calls new elections.

"Today, January 23, 2019, I swear to formally assume the powers of the national executive as president in charge of Venezuela," he told the cheering crowd.

Guaido, 35, said he was taking the politically risky step just two weeks after Maduro took his own oath to a second six-year term because it was the only way to rescue Venezuela from "dictatorship" and restore constitutional order.

"We know that this will have consequences," he shouted, moments before quickly slipping away to an unknown location amid speculation he would soon be arrested. "To be able to achieve this task and to re-establish the constitution we need the agreement of all Venezuelans."

Maduro did not immediately respond. But socialist party boss Diosdado Cabello, widely seen as the No. 2 most-powerful person in the country, blasted the U.S. and its "lackeys" in the region for trying to topple Maduro by violent means.

"The Bolivarian revolution doesn't have an expiration date," he told a crowd of red-shirted government supporters who then headed to the presidential palace, where Maduro was expected to address them.

Guaido's declaration came as tens of thousands of anti-government demonstrators poured into the streets Wednesday accusing the embattled Maduro of usurping power and demanding he step down as the country reels from a crushing economic crisis that has forced millions to flee or go hungry.

Large crowds gathered in Caracas waving flags and chanting "Get out Maduro!" in what was the largest demonstration since a wave of unrest that left more than 120 dead in 2017. "Join us!" the protesters cried out to a line of officers wearing helmets and carrying shields. "You are also living this crisis!"

Pro-government demonstrators also marched in the capital, at times crossing paths with opposition protesters and shouting "sell outs" and "traitors." National guardsmen launched tear gas at anti-government protesters in the middle-class neighborhood of El Paraiso but for the most part the marches continued without conflict.

Wednesday's protest was considered a crucial test for the reinvigorated opposition as it seeks to send a forceful message that Maduro no longer has the people's backing and appeals to the military and the poor to shift loyalties that until recently looked solidly behind the president. The protests were called to coincide with an historic date for Venezuelans — the anniversary of the 1958 coup that overthrew military dictator Marcos Perez Jimenez.

President Donald Trump, Vice President Mike Pence and Secretary of State Mike Pompeo all issued statements proclaiming U.S. recognition of Guaido and saying the U.S. would take all diplomatic and economic measures necessary to support a transition to a new government.  

"The people of Venezuela have courageously spoken out against Maduro and his regime and demanded freedom and the rule of law," Trump said in his statement.

Driving the crisis was Maduro's decision to ignore international opposition and take the presidential oath on Jan. 10 for a second term widely considered illegitimate after his main opponents were banned from running against him.

The events on Wednesday followed a whirlwind week that saw an uprising by a tiny military unit put down by government forces, fires set during protests in poor neighborhoods and the brief detention by security forces of Guaido.

Guaido, who took the reins of leadership in the opposition-controlled Congress from a long list of better-known predecessors who have been exiled, outlawed or jailed, was dragged from an SUV just over a week ago by intelligence agents but was quickly released amid an international outcry.

Over the last two nights, Venezuelans angry over their country's spiraling hyperinflation, and food and medical shortages have gathered in the streets banging pots and pans and setting up barricades in protest. In the city of San Felix, residents set fire to a statue of Maduro's mentor and predecessor, the late Hugo Chavez.