A videograb of the attack shows Juan Guaido in ripped off shirt.
The leader of the US-backed opposition in Venezuela was physically attacked on Saturday during a visit to a rural community, according to members of his parallel government, who accused a group of ruling party associates of carrying out the assault.
A photo accompanying the opposition statement shows Juan Guaidó being held back as people gather around him and someone rips his shirt off.
The parallel government said the group, which was associated with the United Socialist Party of Venezuela, known as PSUV, "hit and insulted” Guaidó, who is on a tour around the South American country seeking to unite and organize his party ahead of a planned primary election.
In an Instagram video on Saturday night, Guaidó characterised the attack as an "ambush” at a plant nursery in San Carlos, a community about 270 kilometres southwest of Caracas, the capital. But he added that it won't deter him from continuing to be "on the street.”
"Those who attacked today, these members or leaders of the regime’s party," should accept responsibility for the incident, he said.
PSUV leaders, who traditionally issue statements on social media or state television, did not immediately respond.
Last week, Guaidó's supporters were met by a barrage of flying plastic chairs and fisticuffs from allies of President Nicolás Maduro in the western city of Maracaibo.
The US and other nations recognize Guaidó as Venezuela’s interim president. They withdrew recognition of Maduro after accusing him of rigging his 2018 re-election as president.
At the time, Guaidó drew enormous crowds of backers into the streets, but much of the momentum has evaporated. His popularity has dropped from about 60% three years ago to under 15% in February.
Brian Nichols, the US assistant secretary of state for Western Hemisphere affairs, on Saturday condemned what he described as an "unprovoked attack” on Guaidó.
"This egregious attack risked lives; those responsible for the assault should be brought to justice,” he said.