Venezuela's ruling Socialist Party legislators called a trip by Brazilian senators to visit jailed opponents of President Nicolas Maduro "abusive" and "meddling" on Friday.
The Brazilian delegation's visit on Thursday was cut short after they said their minibus was stoned by Maduro supporters and roads were blocked, forcing them to return to the airport and fly back the same day.
The Brazilian senators had hoped to visit detained politicians including hardline leader Leopoldo Lopez, on a partial hunger strike in a military prison, and Caracas mayor Antonio Ledezma, who is under house arrest.
Members of Maduro's Socialist Party said the half-dozen Brazilians were part of a right-wing international conspiracy.
"There is an ill intention from these political groups, not only to come and threaten ... but also to torpedo the good relations between Venezuela and Brazil," National Assembly Vice President Tania Diaz told reporters. "They want the same as Venezuela's extreme right: to isolate the country and sabotage integration."
Foreign support for opposition leaders is a sensitive issue for the Maduro government, which views them as U.S.-backed agitators intent on fomenting a coup.
A Venezuelan representative to the Latin American Parliament said a complaint against the Brazilian senators would be made at a June 30 meeting of its rights commission.
"We are going to denounce this undoubted meddling, rude, arrogant and disrespectful policy," Marelys Perez said.
Venezuelan opposition leaders, who have formed a broad coalition called Democratic Unity and are campaigning ahead of a parliamentary election later this year, said the incident illustrated the dictatorial nature of Maduro's government.
"The Brazilian senators came yesterday to check on Venezuelans' human rights and left knowing even their own rights were violated," opposition coalition head Jesus Torrealba said.
Brazil is a major investor in Venezuela, and ties have been good since Maduro's predecessor Hugo Chavez took office in 1999.
But President Dilma Rousseff has faced increasing internal pressure to distance herself from Maduro.
Brazil's government condemned the incident.
Its foreign minister called his Venezuelan counterpart to demand an explanation of the incident, and the Venezuelan ambassador to Brazil was also called in to explain.
Lopez, 44, who has been digesting liquids only for the last 26 days, according to his family, was accused last year of stirring violence around anti-Maduro protests that killed more than 40 people, including government and opposition supporters.
Ledezma, 60, is accused of conspiracy. Both men deny the charges.