The clash heightened tensions on the same day the Venezuelan government expelled foreign diplomats for the second time in a month.
More than 100 men on motorcycles carrying pipes and rocks swarmed the area and some tried to force their way into buildings.
Residents screamed "murderers, murderers" from rooftops and the motorcyclists taunted them from below, urging them to come down and fight.
When National Guardsmen arrived to secure the area, a 25-year-old sergeant was shot through the neck and killed.
At least 21 people have been killed in related violence, by the government's count, in the country's worst unrest in years.
President Nicolas Maduro's administration shows no signs of crumbling from several weeks of nearly daily demonstrations, but the country appears in a stalemate.