A 17-year-old boy and a 23-year-old woman died after being shot Wednesday during massive protests, and a soldier outside Caracas was said to have been killed, bringing to eight the number of people killed this month in a mounting political crisis.
Riot police fired tear gas to force back stone-throwing demonstrators as hundreds of thousands of people fed up with food shortages and demanding elections joined protest marches in Caracas and several other cities.
Thousands of Maduro's supporters held a counter-rally in central Caracas.
The opposition has accused Maduro of letting state forces and gangs of armed thugs violently repress demonstrators as he resists opposition pressure for him to quit.
Despite Wednesday's deadly violence, his opponents displayed their determination to ratchet up the pressure by calling for renewed protests on Thursday.
"Today there were millions of us," senior opposition leader Henrique Capriles told a news conference late Wednesday.
"Tomorrow even more of us have to come out."
The 17-year-old was shot by gunmen on motorbikes who also threw tear gas canisters into a crowd of protesters, Amadeo Leiva, head of the Clinicas Caracas Hospital which treated him, told AFP.
The 23-year-old woman, Paola Ramirez, died after being shot in the head in the western city of San Cristobal, the state prosecution service said later in a statement.