The actions in Caracas, amid rapidly rising tensions across the country, took place ahead of a planned major march in the capital Tuesday by student-led protesters and and followers of opposition leader Leopoldo Lopez and a counter-demonstration by pro-regime oil workers called by President Nicolas Maduro.
The scuffle between security forces and the activist crowd came during a national guard raid of the opposition Popular Will party headquarters, led by Lopez, who Maduro accuses of murder and terrorism in relation to deadly demonstrations last week.
The student-led protests are calling for Maduro to resign and complaining about economic hardships, soaring crime and rampant corruption in a country whose annual inflation tops 50 percent.
Maduro alleges Lopez is behind a "right-wing fascist" plot to overthrow him.
Lopez claims no connection to the violence, which left three people dead Wednesday.
He has been in hiding since Friday but asked followers in a YouTube video Sunday to join him in a peaceful protest Tuesday as he marches to the state prosecutor's office in downtown Caracas to demand the regime release students jailed in demonstrations two weeks ago.
Justice Minister Miguel Rodriguez Torres said Monday Lopez had no legitimate business to conduct at the prosecutor's office.
The guardsmen raid came shortly after four unidentified T-shirted men with guns -- three wearing dark helmets -- stormed into the Popular Will headquarters.
The men, guns drawn, searched four occupants in a waiting room for weapons and demanded answers to questions before one of the men kicked down a door leading to a backroom, a security video indicated.
About two-dozen people in the backroom later went into the waiting room as the T-shirted men left, the video indicated.
The national guard raid shortly afterward came as phalanxes of guardsmen lined the street outside the headquarters to keep student-led protesters away, a separate video and witness accounts indicated.
Some witnesses said on Twitter some guardsmen used teargas and flash grenades to keep protesters away.
The armed guardsmen inside the headquarters handcuffed City Councilman Dario Ramirez of the centrist Popular Will party and tried to take him away, but students and other activists outside managed break through and scuffle with the guardsmen, wrestle him free and whisk him away, witnesses said.
"It is impossible to overstate the gravity of what happened at the party headquarters," Ramen Guillermo Aveledo, executive secretary of the opposition electoral Coalition for Democratic Unity, said afterward in remarks quoted by Venezuelan newspaper El Nacional.
Aveledo accused Maduro with ordering the raid and the attempted capture of Ramirez, which he called an "intolerable abuse."
Around the same time a truck driven by an oil worker for state-owned Petroleos de Venezuela drove into a separate student protest, hitting two students, including a 17-year-old naval engineering student who died Monday night, local reports indicated.
The other student, who was unidentified, had both legs broken, Venezuelan newspaper El Universal said.
"I'm shocked, speechless," a Twitter message by someone using the name Maria Farinha said.
"My infinite condolences," lawyer Juan Ferreira wrote, adding, "Please, out of respect, do not put more photos [of the young man] on the social networks."
The death of Jose Ernesto Mendez brought the death toll to four, but opposition officials say the death toll may be twice that high.
During Tuesday's planned march, Lopez aides changed the route to avoid a confrontation with the pro-regime oil workers.
Lopez asked for demonstrators to "go dressed in white to signify our commitment to peace."
"We own our future! We are on the right side d history, we are on the side of justice, we are on the side of truth!" he said on Twitter late Monday night.