The current protests are the biggest that the Maduro government has faced in its 11 months in power.
The latest death came Monday, when a 17-year-old was hit by a truck and killed at a protest in the northeastern city of Carupano, a government official said.
Lopez's party, Popular Will, has accused the government of being responsible for violence during the protests.
At Tuesday's rally, Maduro stressed that the socialist revolution he now leads is peaceful and democratic.
"What I want is peace, dialogue, understanding, coexistence," Maduro said. "It is what I want and what I am doing."
But another opposition leader said that the government's actions paint a different picture.
"The latest actions we've seen from the government indicate that far from fomenting a climate of peace, (it) is trying to fortify the climate of confrontation and violence that the world has seen in images," former presidential candidate Henrique Capriles told CNN en Español.
Capriles has backed away from calling for massive protests, saying they are ineffective and play into the government's narrative, but he said Lopez has his support.
"The protest will continue as long as the government gives no sign of resolving the problems of the Venezuelans," Capriles said.
At least seven people were injured when gunfire erupted during a protest Tuesday in the northern city of Valencia on Tuesday, CNN affiliate Globovision reported. One of them, according to two officials who did not wish to be identified, was a local beauty queen.