Bolivian security forces clashed with supporters of former president Evo Morales in a central town Friday, leaving at least five people dead, dozens more injured and escalating the challenge to the country's interim government to restore stability.

The director of the Mexico Hospital in the town of Sacaba, Guadalberto Lara, told The Associated Press that most of the dead and many of the 75 injured had bullet wounds. Witnesses said police opened fire on protesters calling for the return of Morales from exile in Mexico.

"It's very unfortunate," Lara said, calling it the worst violence he's seen in his 30-year career.

Thousands of largely Indigenous protesters had gathered peacefully in Sacaba in the morning. But fighting began when many tried to cross a military checkpoint near the city of Cochabamba, where Morales' supporters and foes have clashed for weeks.

Many details of the violence in Sacaba remained unclear.

Supporters of Bolivia's former president Evo Morales protect themselves from tear gas launched by the police in La Paz on Friday. (Natacha Pisarenko/Associated Press)

Emeterio Colque Sanchez, a 23-year-old university student who participated in the protest, said he saw the bodies of several protesters who had been fatally shot.

Sanchez, who spoke from the site of the clashes, said about two-dozen injured people were taken to a hospital.

Another protester, 40-year-old Franco Rios, also said he saw the bodies of several protesters.

Para justificar el golpe, Mesa y Camacho nos acusaron de "dictadura". Ahora su "presidenta" autonombrada y su gabinete de abogados defensores de violadores y represores, masacra al pueblo con las FFAA y la Policía como la verdadera dictadura. <a href="https://twitter.com/hashtag/NoAlGolpeDeEstadoEnBolivia?src=hash&ref_src=twsrc%5Etfw">#NoAlGolpeDeEstadoEnBolivia</a> <a href="https://t.co/FiDDor2idk">pic.twitter.com/FiDDor2idk</a> —@evoespueblo

Another witness, 27-year-old Rocio Rocha Perez, said she arrived at the Sacaba hospital as ambulances brought the injured. Many people were covered in blood and that the scene was chaotic as medical staff rushed to treat the severely injured, she said.

Morales, who has been granted asylum in Mexico, said on Twitter that a "massacre" had occurred and he described Bolivia's interim government as a dictatorship.

In the capital of La Paz, riot police fired tear gas at rock-throwing demonstrators. Elderly people and children were caught in the violence and tried to seek shelter in businesses that had been shut behind metal sheets to protect against looters.

'I'm still president'

The violence came as Bolivia's interim leader said Morales will face possible legal charges for election fraud if he returns home, even as the ousted leader contended he is still president despite resigning after massive protests against him.

Interim president Jeanine Anez had said on Thursday that Morales would not be allowed to participate in upcoming presidential elections meant to heal the Andean nation's political standoff.

Morales stepped down on Sunday following nationwide protests over suspected vote-rigging in an Oct. 20 election in which he claimed to have won a fourth term in office. An Organization of American States audit of the vote found widespread irregularities.

Interim President Jeanine Anez, left, had said that former president Evo Morales would not be allowed to participate in upcoming presidential elections. (Marco Bello, Edgard Garrido/Reuters)

On Thursday, Morales told The Associated Press in Mexico that while he had submitted his resignation, it was never accepted by Congress.

"I can say that I'm still president," he said.

Morales said he left because of military pressure — the army chief had "suggested" he leave — and threats of violence against his close collaborators.

Anez dismissed the explanation.

"Evo Morales went on his own. Nobody kicked him out," she said at a news conference.

"He knows he has accounts pending with justice. He can return but he has to answer to justice for electoral fraud," she added. "Justice has to do its work without political pressures."

Protesters set up blockades

Supporters of Bolivia's first Indigenous president have been staging their own disruptive protests since his ouster, setting up blockades that forced closure of schools and caused shortages of gasoline in the capital. Long lines formed outside some gas stations in La Paz after blockades in the nearby city of El Alto, a major distribution point for fuel.

"There's no gas," said Efrain Mendoza, a taxi driver from El Alto, who was forced to buy gasoline on the black market at twice the regular price on the pump.

"Products are scarce. There's no meat, no chicken, people are making long lines. It's all because of the blockades," he said. "There's division in Bolivia. It's exasperating."

Demonstrators build a barricade during clashes with security forces in La Paz on Friday. (Marco Bello/Reuters)

Anez, the highest-ranking opposition official in the Senate, proclaimed herself president, saying every person in the line of succession ahead of her —all of them Morales backers — had resigned. The country's Constitutional Court issued a statement backing her claim that she didn't need to be confirmed by Congress, a body controlled by Morales' Movement Toward Socialism party.

Much of the opposition to Morales sprang from his refusal to accept a referendum that would have forbidden him from running for a new term.

Morales had upended politics in this nation long ruled by light-skinned descendants of Europeans by reversing deep-rooted inequality. The economy benefited from a boom in prices of commodities and he ushered through a new constitution that created a new Congress with seats reserved for Bolivia's smaller indigenous groups while also allowing self-rule for all indigenous communities.

But many people became disenchanted by his insistence on holding on to power.