The socialist president’s announcement came amid dueling pro-government and student-led opposition demonstrations held in different parts of the capital, Caracas.

Lopez “ordered all these violent kids, which he trained, to destroy the prosecutor’s office and half of Caracas and then goes into hiding,” Maduro told thousands of supporters at a rally to denounce what he called a U.S.-backed, “fascist” plot to oust him from power. “Turn yourself in coward.”

U.S. officials have denied plotting to oust Maduro, and on Saturday Secretary of State John Kerry expressed concern over the rising tensions and violence surrounding the protests.

“We are particularly alarmed by reports that the Venezuelan government has arrested or detained scores of anti-government protesters and issued an arrest warrant for opposition leader Leopoldo Lopez,” Kerry said in a statement. “These actions have a chilling effect on citizens’ rights to express their grievances peacefully.”

Maduro said security forces acting on a Feb. 12 arrest order are now looking for Lopez, who hasn’t been seen since a Wednesday night press conference in which he vowed that anti-government street protests would continue.

Venezuela’s president didn’t mention Lopez by name, referring to him only by a frequently-used disparaging nickname, The Throne, to denote what he considers the Harvard-trained politician’s haughty political ambitions.

Still, his comments seemed to confirm a report Thursday by local newspaper El Universal, which published what it said was a leaked copy of an arrest order for Lopez on charges ranging from vandalism of public property to terrorism.

While Cabinet officials and Maduro have blasted Lopez all week as the mastermind of Wednesday’s student-led protests that ended in clashes with police and pro-government militias, no official had until now confirmed authorities were looking to arrest him.

Aides to Lopez denied he’s ducking arrest and say he remains in the country. His lawyers, who’ve been unable to gain access to the alleged arrest order, have urged him to refrain from making public statements until one materializes.

Lopez, a former mayor, is the most prominent of a group of hard-liners that have challenged two-time presidential candidate Henrique Capriles for leadership of anti-Maduro forces.

In an apparent bid to dampen anti-government demonstrations, which have been held off-and-on since Wednesday, Maduro said he had ordered the suspension of metro and bus service in the Chacao area of the capital where the protests are centered.

“We can’t have a moment of weakness because we are trying to defeat a fascist movement that wants to end the country we have,” said Maduro, the hand-picked successor to the late Hugo Chavez whose government has been struggling with shortages and high inflation.

In Chacao, meanwhile, Venezuelan security forces used tear gas to disperse hundreds of university students who were gathering to demand justice for two students killed during Wednesday’s demonstration.

For the past three days student protesters had occupied the main highway through Caracas for several hours, blocking traffic to press their demands.

Ramon Muchacho, the mayor of Chacao, said that on Saturday the students were walking “peacefully toward the highway … when they were repelled by tear gas.”

The students responded by throwing rocks at police and regrouping nearby.

Muchacho later tweeted that 10 people had been injured, none with bullet wounds.

“We are not going to give in or kneel. We are going to continue in the streets, fighting for Venezuelans and the youths who want a democratic country, with free media that aren’t censored or self-censored, with justice and equity,” said Juan Requesen, a student leader at the Universidad Central de Venezuela.

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By Joshua Goodman