Young people clashed with police in the streets of the Venezuelan capital in an angry response to security forces dismantling four tent cities maintained by anti-government demonstrators.
Officials reported one officer was killed and another injured.
The bloodshed came after hundreds of police and troops arrested 243 student protesters during pre-dawn raids on camps in front of United Nations offices and in better-off neighbourhoods largely opposed to President Nicolas Maduro's socialist government.
Interior Minister Miguel Rodriguez Torres presented homemade mortars, guns and Molotov cocktails that he said were seized at the camps and used to carry out "terrorist" acts against security forces.
"This shows there was an entire logistical apparatus in place," Rodriguez Torres said, seeking to counter claims that the anti-government movement has been peaceful and spontaneous.
Dozens of anti-government activists erected barricades throughout the day to express solidarity with the jailed students, setting off clashes with police. One officer was killed and another wounded by gunfire.
Maduro said the officer was killed by a sniper while police cleared the streets of debris in the leafy Chacao district where the UN office is.
"He was protecting the community of Chacao and was killed vilely by these right-wing assassins," Maduro said at an event in Caracas to deliver homes to low-income families.
The death brought to 42 the number of people on all sides killed since anti-government protests began to shake the South American nation in February.
The dismantling of the camps was announced just hours before a top opposition leader, Leopoldo Lopez, was scheduled to appear in court after being in custody since February.
The hearing on whether he should go on trial on charges of inciting violence at anti-government protests was suspended and he returned to a military prison almost as soon as he arrived at the courthouse.
Witnesses near the UN office said hundreds of National Guardsmen began arriving after 3am. They were greeted by neighbours who launched objects and insults from balconies.
Rodriguez Torres said the operation was carried out cleanly, with security forces relying on the element of surprise rather than aggressive force to round up the protesters.
He said the detainees would be charged. Prosecutors have 48 hours to bring detainees before a judge and either charge or release them. But in recent months officials have often ignored the rules and held protesters incommunicado for longer periods.
Hours after the raids, a scattered detritus of shoes, clothes and destroyed banners littered the streets where the makeshift campground once stood. A few dozen neighbours built barricades to block traffic, demanding the release of the students.
"How can this be allowed when the constitution guarantees the right to peaceful protest," said Anais Serrano, a real estate agent. "These kids weren't doing anything bad."