Venezuelan riot police have used teargas and water cannon to break up protests in the capital Caracas.
Violence broke out on Saturday after supporters and opponents of the Venezuelan president Nicolas Maduro staged rival rallies, AFP news agency reported.
It was the latest in a wave of demonstrations that has left three people dead, 60 injured and about 100 arrested.
On Saturday Maduro told thousands of people attending his rally that a police manhunt was underway for the opposition leader, Leopoldo Lopez.
He said Lopez had "ordered all these violent kids, which he trained, to destroy the prosecutor's office and half of Caracas and then goes into hiding".
He denounced what he called a US-backed "fascist" plot to oust him from power and challenged Lopez: "Turn yourself in coward."
Rules for television
On Saturday anti-government protesters threw objects and taunted the police, who responded with volleys of teargas and a water cannon truck, or "whale" as Venezuelans call it.
Most were students, who have spearheaded nearly two weeks of protests against Maduro. Rampant crime, soaring inflation and basic goods shortages are their main grievances.
The protesters have demanded that Maduro step down, although opposition leaders have said that political conditions are not favourable at present for the president's exit.
Seeking to quell the unrest, Maduro late on Friday announced a 10-point plan to crack down on crime that includes disarming the population, increased police patrols, as well as unspecified "clear rules for television".
In a statement on Saturday, John Kerry, the US Secretary of State, said: "We are alarmed by reports that the Venezuelan government has arrested or detained scores of anti-government protestors and issued an arrest warrant for opposition leader Leopoldo Lopez. These actions have a chilling effect on citizens' rights to express their grievances peacefully."
Despite having the world's largest proven reserves of crude oil, the country has severe economic problems and a deep divide between rich and poor.