Venezuela President Nicolas Maduro announced Saturday the country will restrict the activities of U.S. diplomats, shrink the size of the U.S. Embassy staff and require Americans to apply for visas if they want to visit.

Maduro said at a protest against imperialism that “gringo” meddling had forced him to adopt the series of limitations that also includes requiring U.S. diplomats to seek approval from the Foreign Ministry before conducting meetings.

The new tourist visa requirement was imposed for national security reasons after authorities had detained several Americans, including a U.S. pilot, who allegedly were involved in espionage, Maduro said.

About an American pilot possibly being held in Venezuela, a State Department official told Fox News “we are still looking into it.”

Venezuela released four missionaries from North Dakota earlier Saturday. They were detained for several days for unknown reasons. Venezuela banned them from the country for two years.

Maduro also addressed President Obama directly Saturday, saying the U.S. president has "arrogantly" refused to engage in conciliatory talks.  

"I'm very sorry, Mr. President, that you have gone down this dead end," he during a speech that all Venezuelan television and radio stations were required to carry.

Venezuela plans to charge Americans the same tourist visa fees that the U.S. charges Venezuelans. The payment will have to be made in dollars. Maduro said he welcomes all comers.

A senior administration official in Washington said the U.S. government had not received any communications from Venezuela and couldn't comment yet on the new restrictions, which come after the U.S. recently imposed a travel ban on a list of top Venezuelan officials accused of human rights violations.

The official also again rejected Maduro's claims that the U.S. is plotting against Venezuela.

"We are aware of reports that President Maduro repeated a number of inflammatory statements about the United States during a televised political rally today. The continued allegations that the United States is involved in efforts to destabilize the Venezuelan government are baseless and false," said the official.

Earlier in the day, Venezuelans participated in two different protests. One rally called for the attention to a crackdown on government opponents and another showed support for the socialist administration.

Government supporters marched to the presidential palace to express their rejection of imperialism and commemorate the 26th anniversary of a convulsion of violence in Caracas widely seen by government backers as evidence of the brutality of pre-socialist administrations.

Opposition activists, meanwhile, gathered to denounce the arrest of Caracas Mayor Antonio Ledezma earlier this month and the death on Tuesday of a teenager who was shot during an anti-government protest.

Fox News’ Lucas Tomlinson and The Associated Press contributed to this report