The office of the United Nations High Commissioner for Human Rights has raised concerns about curbs to civil liberties and reports on the use of “excessive” force by police and military officers in El Salvador after a recent wave of gang violence.

In a statement on Tuesday, spokeswoman Liz Throssell said Salvadoran police and military forces deployed to gang strongholds under a state of emergency have resorted to “unnecessary and excessive use of force”.

She said “more than 5,747 people have been detained without an arrest warrant” since the state of emergency was adopted in late March, “and some have reportedly been subjected to cruel, inhuman or degrading treatment”.

“Now, we recognise the challenges posed by gang violence in El Salvador and the State’s duty to ensure security and justice. However, it is imperative that this is done in compliance with international human rights law,” Throssell said.

El Salvador’s parliament approved a “state of exception” on March 27 in the aftermath of more than 80 weekend killings, which the government blamed on criminal gangs. Sixty-two people were killed in a single day – the highest, one-day tally in decades.

The state of emergency suspends certain civil liberties, including the right to association and the right to legal counsel, and prompted calls from civil society groups for President Nayib Bukele’s administration to ensure international human rights standards are met.

Bukele said this week that 6,000 suspected gang members had been arrested since the order came into force.

The two main criminal groups in the country, Mara Salvatrucha – more commonly referred to as MS-13 – and Barrio 18, have an estimated 70,000 members between them, and several thousand are already in Salvadoran prisons.

The president, who last week warned that gang membership leads to “prison or death“, on Monday also pledged to deny food in prison to gang members who take “revenge” on the population over his policies – a threat he repeated Tuesday.

Members of Bukele’s governing party last week pushed through substantial increases in prison sentences in response to the violence.

Under the new rules, convicted gang lords will now be sentenced to 40 to 45 years in jail, compared with six to nine years previously, while other gang members will be sentenced to 20 to 30 years, up from three to five years earlier.

In Tuesday’s statement, Throssell said the UN office was “deeply concerned about certain amendments to criminal law and criminal procedure” in El Salvador, including the imposition of higher sentences and the weakening of due process guarantees.

“Criminal trials can now be held in absentia, in the case of alleged gang members, or presided over by so-called ‘faceless’ judges, and that is, judges whose identity remains confidential, while the previous two-year limit to pre-trial detention has been eliminated,” she said.

Throssell also said teenagers associated with gangs who are found guilty of serious offences can now be sentenced as adults, and they can be forced to serve their sentences in adult prisons rather than juvenile detention centres.

“We remind El Salvador that the right to life, the right not to be subjected to torture, principles of fair trial and the presumption of innocence, as well as the procedural safeguards that protect these rights, apply at all times, even during states of emergency. This is especially with regard to children,” she said.

El Salvador registered 1,140 murders in 2021 – an average of 18 deaths per 100,000 inhabitants – a decline from the 1,341 registered the previous year and the lowest figure since the country’s civil war ended in 1992, according to official data.