Opposition leaders are demanding immediate presidential ele.
The blockades of major roads in Caracas is part of the opposition's strategy to vary tactics and keep up momentum in popular calls against the president. Diego Hernandez, 33, and Luis Alviarez, 18, were killed in Tachira, while Yeison Mora Castillo, 17, died near a protest farther east in the state of Barinas on Monday.
State security launched tear gas and rubber bullets at protesters in at least three other cities.
Monday saw the latest in weeks of violent clashes as opponents mounted fresh demonstrations against President Nicolas Maduro.
On Monday, the Organization of American States voted to hold a rare foreign ministers' meeting later this month to discuss the crisis. Authorities were also investigating a shooting in Carabobo that left two officers injured, one critically.
Protesters also oppose his plans to elect an assembly - and do it sidestepping the country's political parties - to overhaul the constitution, dismissing it as a way to put off elections. More than three dozen people have died in a month and a half of protests.
At least 90 people were arrested during Monday's unrest, according to a local rights group.
More than three dozen people have been killed and hundreds injured in protests that erupted after the government-stacked Supreme Court issued a ruling March 29 nullifying the opposition-controlled National Assembly, a decision it later reversed amid a storm of global criticism and outrage among Venezuelans. Polls show the majority of Venezuelans want Maduro gone as violent crime soars and the country falls into economic ruin. Maduro and top administration leaders contend the OAS is meddling in Venezuela's domestic affairs, infringing on its sovereignty and trying to remove the government from power.
Their demonstrations, and those of Maduro's backers, have escalated since the government-friendly Venezuelan Supreme Court's late-March attempt to strip the National Assembly of its legislative powers and since Maduro's May 1 call for a new constitution. More than three-dozen people have been killed, hundreds injured and as many as 2,000 detained in almost seven weeks of protests. Demonstrators assembled a giant rosary with balloons hanging from a Caracas highway overpass.
"We are against this fraudulent process", Capriles said on his radio broadcast.
A 27-year-old police officer is being charged in connection with Mr Hérnandez's death, the prosecutors' office announced on its Twitter account.
Venezuela is mired in an economic crisis that has caused shortages of food, medicine and other basics in the oil-rich country. The opposition maintains state security and civilian-armed pro-government groups known as "colectivos" are responsible for the bloodshed.
The current wave of protests, which attracted hundreds of thousands of demonstrators on some days, has drawn greater support from the poor.