Supporters of Venezuela's President Nicolas Maduro attend a pro-government rally, one holding a painting of independence hero Simon Bolivar in Caracas, Venezuela on Feb. 15, 2014. Alejandro Cegarra/AP

The White House on Monday denied allegations that it had helped organize protests against the administration of Venezuelan President Nicolas Maduro.

"As we have long said, Venezuela’s political future is for the Venezuelan people to decide. We urge their government to engage all parties in meaningful dialogue," said U.S. State Department spokeswoman Jen Psaki.

Maduro said State Department official Alex Lee, in a phone conversation with Venezuela's ambassador to the Washington-based Organization of American States, warned against serious consequences with international ramifications for arresting Leopoldo Lopez, who Maduro has accused of mounting a "fascist" plot to oust the socialist government two months after it won mayoral elections by a landslide.

The Obama administration has expressed support for Lopez.

"These are unacceptable, insolent demands," Maduro said during a televised address Sunday night. "I don't take orders from anyone in the world."

Maduro on Sunday ordered the expulsion of three U.S. Embassy officials who he said had been conspiring against his government.

Maduro didn't identify the consular officials, but said intelligence officials who tailed them for the past two months found evidence they were trying to infiltrate Venezuelan universities, a hotbed of recent unrest, under the cover of doing visa outreach.

Psaki said she had "not received any formal notification" that Venezuela had expelled three U.S. diplomats.

Sunday's expulsion of U.S. diplomats was the third by Maduro.

In March, hours before announcing the death of President Hugo Chavez, he expelled two U.S. diplomats while suggesting the United States might have been behind the leader's cancer. Then in a fiery speech last September, he ordered the most senior U.S. official in Venezuela and two others to leave, for allegedly helping opponents sabotage the electrical grid.

The Harvard-educated Lopez has been at the center of rising tensions in Venezuela since he led the biggest demonstration yet against Maduro's 10-month-old government, mobilizing more than 10,000 people on Wednesday to protest hardships ranging from rampant crime to 56 percent inflation.

The Venezuelan government blamed him for the mayhem that erupted after the rally ended when a group of students battled with security forces and armed pro-government militias, leaving three dead.

In his TV speech, Maduro called for a march by oil workers Tuesday beginning at the same central plaza in Caracas where Lopez said he would rally with supporters dressed in white the same day, setting up the potential for clashes between the opposing forces.

Lopez announced his plans in a video a few hours before Maduro's speech, saying he didn't fear arrest but accusing authorities of trying to violate his constitutional right to protest Maduro's government.

His comments came after security forces raided his home and that of his parents over the weekend, seeking to serve an arrest order. Lopez wasn't at either residence when the officials arrived around midnight to the sound of banging pots and pans by neighbors protesting what they consider an arbitrary detention order.

Lopez is the most prominent of a group of opposition hard-liners who are challenging two-time presidential candidate Henrique Capriles for leadership of the anti-government movement.

Maduro considers him a puppet of U.S. ambitions to regain dominance over South America's largest oil-producing economy.

Al Jazeera and The Associated Press