CARACAS, Venezuela (AP) -- National Guard troops beat dozens of opposition supporters inside a barracks for refusing to accept the government-certified electoral victory of Hugo Chavez's heir, a leading human rights lawyer charged Thursday in what he called Venezuela's worst political repression in six years.
Alfredo Romero said his group's lawyers also compiled evidence supporting opposition activists' claims that National Guard troops had used excessive force against protesters, including shooting some point-blank with plastic shotgun pellets.
As details of the crackdown emerged, Nicolas Maduro prepared to be sworn in as president and the speaker of the National Assembly again threatened to bar the opposition from its only remaining political platform, the legislature, unless it recognized Maduro's legitimacy.
Romero said the beatings occurred at National Guard barracks No. 47 in the western city of Barquisimeto after at least 300 protesters were arrested across Venezuela for backing opposition candidate Henrique Capriles' demand for a recount of all the votes cast Sunday.
Interrogators "put baseball caps on these kids' heads with a pro-government insignia ... and made them say they recognized the Maduro government, and if they said 'No' they were beaten," Romero said, adding that most of the detainees ranged in age from 15 to 22.
Asked about the allegations, Interior Ministry spokesman Jorge Galindo called them "totally false, absurd and without basis." He said the detainees, though in a military barracks, were being overseen by ministry officials to "guarantee their rights."
Romero called the crackdown Venezuela's worst since Chavez shut down the opposition TV station RCTV in 2006 when more than 250 people were arrested. His 12-year-old group, Foro Penal Venezolano, has more than 200 lawyers who represent without charge people they consider political prisoners.
He said the group has complained to the Inter-American Human Rights Commission, whose rulings Venezuela's government no longer recognizes, and is preparing a complaint to the International Criminal Court.
One of the worst cases of excessive force this week occurred in the central city of Valencia, members of the opposition's youth wing said in Caracas.
They said National Guardsmen fired plastic pellets at extremely close range at a group protesting the regime-friendly National Electoral Council's decision to ratify the victory of Nicolas Maduro.
Maduro is to be sworn in Friday in the National Assembly at a ceremony being boycotted by the opposition because its deputies are not being allowed to address the body unless they recognize his presidency as legitimate.
The government says 15 countries including Iran, China and Saudi Arabia were sending high-level delegations. Brazil said its president, Dilma Rousseff, was attending as was Argentina's Cristina Fernandez, but it was not clear whether the president of neighboring Colombia, Juan Manuel Santos, would attend.
On Thursday, Maduro headed to Lima, Peru, for an evening meeting of presidents of the Union of South American Nations, UNASUR, to discuss Venezuela's post-election tensions.
The meeting was convened by Peru's president, Ollanta Humala, who holds the organization's rotating chair, and every leader on the continent save Ecuador's Rafael Correa, who was traveling in Europe, was attending, said Peru's deputy foreign minister, Fernando Rojas.
The youth opposition wing members displayed photographs showing deep, bloody wounds on the skin the hand and arm of Jonny Alvarado, a local leader of the centrist Proyecto Venezuela party who they said had been shot three times in the arm and undergone two surgeries in an attempt to save his hand.
The AP confirmed Alvarado's non-life-threatening injuries with the director of the hospital where he was treated.
At least 10 other activists were hit by pellets, some in the head, but not hurt as seriously, said Carlos Graffe, Proyecto Venezuela's youth leader. He said other protesters were punched or hit with batons by National Guardsmen.
A total of 400 were injured nationwide by authorities and government backers, said Juan Requesens, national coordinator of the opposition's youth wing.
In Monagas state, a group of 30 to 40 protesters was attacked by pro-government forces, then detained by authorities when they tried to flee, said Diego Scharifker, president of the youth wing of the Nuevo Tiempo party. He said virtually all were anti-government, but National Guard members had even swept up a handful of pro-government youth during sweeps of streets.
Romero said other activists described being arrested as they were walking home from peaceful protests.
The government alleges Capriles' backers have incited all the postelection violence, which it says has caused eight deaths and 70 injuries. It also charges the opposition loyalists have burned eight health clinics and several offices of the ruling United Socialist Party of Venezuela.