At least 24 people have been killed and hundreds injured in a week of brutal clashes between protesters and police in Colombia.

What started out as peaceful demonstrations against tax rises have quickly gotten out of hand, fuelled by widespread anger with the rightwing government of Iván Duque.

The UN, the US state department, the EU, Amnesty International and dozens of non-governmental organisations have condemned the violence, which has plunged the Duque administration into the worst crisis of its nearly three years in power.

Gregory Meeks, chair of the US House committee on foreign affairs, said he was “extremely concerned by the brutal [police] response to protests”.

Amnesty said that as well as the deaths and injuries it had registered “arbitrary detentions, acts of torture and sexual violence, and reports of people disappearing”. It said it had evidence of police using assault rifles in the city of Cali and “pointing semi-automatic weapons directly at unarmed demonstrators” in the city of Popayán.

“In another incident, on May 1 in Bogotá, an armoured vehicle was seen firing live ammunition. All such weaponry is prohibited for the dispersal of protests under international standards,” it said.

The UN said it was “deeply alarmed by developments in the city of Cali”, where about half the deaths have been reported. The US state department said it was “deeply saddened by the loss of life” and urged “the utmost restraint by public forces”.

The Duque government said it was using proportionate force to combat violent attacks by protesters armed with guns and Molotov cocktails. It has blamed the violence on leftwing guerrilla groups that were at the heart of the country’s half-century civil conflict. Foreign minister Claudia Blum summoned ambassadors to a meeting on Wednesday to outline the government’s position.

The demonstrations began on Wednesday last week in opposition to the government’s widely panned tax reform plan. Protesters said they could not afford the burden of tax rises after more than a year of lockdowns and lost business caused by the coronavirus pandemic.

The protests were bigger than organisers had expected, prompting them to be extended for several more days. On Sunday, Duque gave in to pressure and withdrew the tax reform bill, saying his government would present an alternative version soon that would shift the burden away from private individuals. The following day, his finance minister Alberto Carrasquilla, the architect of the reform, resigned.

With the bit between their teeth, the protesters have vowed to carry on. They are demanding the government withdraw a draft health bill, which they said would lead to further privatisation of a health system reeling from the pandemic. In rural areas, the focus of protests has morphed from the tax reform to broader demands for greater security and investment.

On Tuesday, Duque extended an olive branch, saying his government would open “a space in which to listen to the citizens and construct solutions”. Government officials explained this meant undertaking a series of meetings with various sectors of society, starting with political parties, mayors and regional governors. Only next week will the government sit down with protest organisers.

“Iván Duque is a lame duck president, and his attempts to deflect the blame on to terrorists, communists, and heavy-handed police officers betray a desperate effort to maintain control of the national narrative as the 2022 election draws near,” said Sergio Guzmán, director of local consultancy Colombia Risk Analysis.

Several political observers said the protests were in effect a resumption of the big anti-government demonstrations of late 2019, which began in Ecuador and Chile and spread to Colombia and elsewhere in the region.

Leftist leaders throughout the Andes, including former Peruvian presidential candidate Verónika Mendoza and current Chilean presidential candidate Daniel Jadue, have expressed solidarity this week with the Colombian demonstrators.

The state ombudsman’s office has confirmed 24 deaths in the week’s protests, 17 of them in Valle del Cauca, the southwesterly province of the country of which Cali is the capital. The other seven deaths were spread among seven provinces, an indication of the breadth of the demonstrations. The ombudsman’s office has confirmed 846 injuries, including 306 civilians.

One local NGO, Temblores, said it had registered 31 deaths at the hands of police, 814 arbitrary detentions and over 1,400 cases of police violence, including sexual violence.

On Tuesday night, protesters firebombed a small police station in Bogotá while 10 police officers were inside. The officers escaped but five were injured, the local government said.

There have also been extensive blockades across the country that have led to fuel and food shortages in some areas, including Cali.

In the town of Tocancipá, north of Bogotá, protesters attacked an ambulance that was trying to take a pregnant woman to hospital in the capital after she went into premature labour. The woman was forced to give birth in the ambulance and the baby died, local officials said.