"The peace-loving Venezuelans feel very, very worried by the irrational, fascist-leaning attitude and actions of a sector of the Venezuelan opposition," he said.
This isn't the first time that bitter protests and counter-protests by supporters and opponents of the government have threatened political stability in Venezuela over the past decade.
Many of Maduro's claims -- of U.S. intervention, of assassination plots -- were also lobbed by the late President Hugo Chavez. Chavez was briefly ousted in a coup in 2002, but otherwise outlasted the protests and repeatedly won re-election and ruled for 14 years until his death last year after a long battle with cancer.
The U.S. State Department has repeatedly denied Venezuela's accusations. Asked whether the United States backs Lopez, Sen. John McCain told CNN Tuesday that his country "backs the people's right to express their will, to object to corruption, the repression of the media and the arrest of political dissidents."
Opposition leader: Government wants confrontation
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.