At least 138 people deported to El Salvador from the United States in recent years were subsequently killed, Human Rights Watch said in a new report that comes as the Trump administration makes it harder for Central Americans to seek refuge in the country.

A majority of the deaths documented by Human Rights Watch in the report, released on Wednesday, occurred less than a year after the deportees returned to El Salvador, and some within days. The organisation also confirmed at least 70 cases of sexual assault or other violence following their arrival in the country.

"As asylum and immigration policies tighten in the United States and dire security problems continue in El Salvador, the US is repeatedly violating its obligations to protect Salvadorans from return to serious risk of harm," HRW wrote.

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The violence underscores the risk faced by people forced to return by US law that mandates deportation of non-citizens convicted of a range of crimes and Trump administration policies that discourage asylum seekers, said Alison Leal Parker, the group's US managing director.

"Our concern is that many of these people are facing a death sentence," Leal Parker said.

Between 2014 and 2018 the US deported about 111,000 Salvadorans back to their homeland, which has long been in the grip of fierce gang violence.

The United Nations reported last year that killings in El Salvador, a majority of them linked to gang conflict, have declined from a peak of more than 6,000 in 2015. But the country still has one of the highest homicide rates in the world.

Meanwhile, the number of Salvadorans seeking asylum in the US grew by nearly 1,000 percent between 2012 and 2017, many citing threats from gangs. Only about 18 percent are granted asylum.

'The risk she faced was being killed'

HRW confirmed the 138 deaths during that period through official records, interviews with families and media accounts but believes the actual toll is much higher, in part because some are not recorded due to the stigma of having been deported from the US. The number of assaults is likely low also because of underreporting in the country of 6.5 million.

The report cites the case of Camila Diaz Cordova, a 29-year-old transgender woman who applied for asylum in the US in August 2017 to escape death threats and extortion by multinational gang Barrio 18.

After her deportation in November 2017, she returned to sex work in San Salvador, the capital, where she was kidnapped and beaten to death by the police, according to a close friend of Diaz Cordova and Salvador's attorney general.

"By losing her bid for asylum or refuge in the United States, or anywhere else, the risk she faced was exactly that: being killed," the friend of Diaz Cordova said in an interview.

People deported from the US get off a bus at an immigration facility in San Salvador, El Salvador [File: Jose Cabezas/Reuters]

Many other deported migrants say their lives are in danger back home.

Luis, 41, worked nearly 20 years in California until he was deported in 2015 after failing to appear for an immigration hearing. Luis, who did not wish to use his full name due to fear of reprisals, found work as a bus driver on the outskirts of San Salvador but was perceived as an outsider and a threat by local gangs.

Gang members shot at him and a bullet struck the bus once, though Luis escaped unscathed.

"They said if they saw me again, they would take me out," Luis told Reuters news agency. The threats have subsided since he began making payments to gangs to be able to drive through their territory, he said.

Cesar Rios, executive director of the Salvadoran Migration Institute, a non-governmental organisation, said no one in the country tracks the deaths of deportees but that he found the data credible, saying it reflects the reality that many are moving back to communities in the grip of the gangs.

"We can say that deporting people to these areas is very difficult and dangerous," Rios said.

President Donald Trump has made his hardline immigration policies a centrepiece of his administration. That has included a policy of forcing asylum seekers from Central America to wait in Mexico while their claims are evaluated or sent back to their homelands if their claim is rejected. Others are sent to Guatemala to seek asylum there instead, despite rights groups warning the country does not have the means to host asylum seekers.

Many of those asylum seekers could previously have been released on parole in the US for a decision that could take a year or more. The Department of Homeland Security says it is trying to make the process more efficient and crack down on fraudulent claims.

But Leal Parker and other critics say this report, and previous efforts that have documented violence against Salvadorans waiting in a Mexican border town for their claims to be processed, show the risks of the Trump administration policy.

"We are deeply concerned by the Trump administration's effort to literally eviscerate the right to seek asylum in the United States," she said.

HRW urged the administration to repeal the policy that requires asylum seekers to wait in Mexico along with the agreements that allow Guatemalans, Salvadorans and Hondurans to be settled in other countries of Central America while seeking refuge. They also want the attorney general to reverse restrictions that made it harder for them to claim US asylum because of threats posed by gangs or gender-based violence.