Bolivia’s political crisis again turned deadly when security forces opened fire on supporters of Evo Morales.
Officials said at least eight people died and dozens were injured in an incident that threatens the interim government’s efforts to restore stability following the resignation of the former president in an election dispute.
Most of the dead and injured in Sacaba, near the city of Cochabamba, had been shot.
Guadalberto Lara, director of the town’s Mexico Hospital who confirmed the fatalities, said it is the worst violence he has seen in his 30-year career.
Angry demonstrators and relatives of the victims later gathered at the site of the shootings, chanting: “Civil war, now.”
Mr Morales, who was granted asylum in Mexico after his November 10 resignation, said on Twitter that a “massacre” had occurred, and he described the interim government led by Jeanine Anez as a dictatorship.
“Now they are killing our brothers in Sacaba, Cochabamba,” he said in another tweet.
At least 13 other people died during weeks of earlier protests against Mr Morales before his departure, according to the Ombudsman’s Office. Several came in clashes between the president’s backers and those accusing him of fraudulently trying to win re-election.
The UN human rights chief, former Chilean president Michelle Bachelet, issued a statement on Saturday calling the latest deaths “an extremely dangerous development”.
She added: “I am really concerned that the situation in Bolivia could spin out of control if the authorities do not handle it sensitively and in accordance with international norms.
“The country is split and people on both sides of the political divide are extremely angry. In a situation like this, repressive actions by the authorities will simply stoke that anger even further and are likely to jeopardise any possible avenue for dialogue.”
Protesters said police fired when demonstrators, including many coca leaf growers who backed Bolivia’s first indigenous president, tried to cross a military checkpoint.
Presidency Minister Jerjes Justiniano accused protesters of using “military weapons”.
Earlier in the day, Ms Anez said Mr Morales would face possible legal charges for election fraud if he returns home from Mexico City.
Ms Anez has also said he would not be allowed to participate in new presidential elections, which are supposed to be held within three months.
The ousted leader, meanwhile, contended this week he is still president since the country’s legislature has not yet approved his resignation.
Mr Morales stepped down following nationwide protests over suspected vote-rigging in an October 20 election in which he claimed to have won a fourth term in office.
An Organisation of American States audit of the vote found widespread irregularities. Mr Morales has denied there was fraud.
Meanwhile, the families of those killed held a candlelight vigil in Sacaba.
A tearful woman put her hand on a wooden casket surrounded by flowers and asked: “Is this what you call democracy? Killing us like nothing?”