PHNOM PENH (Reuters) - Thirty-seven Cambodian deported by the United States arrived in Phnom Penh on Thursday, 32 of them refugees who fled during the rule of the genocidal Khmer Rouge in the 1970s or war that followed their ouster, an aid group said.

Thousands of Cambodian refugees started new lives in the United States after fleeing the Khmer Rouge’s 1975-1979 reign of terror, in which up to 2 million people are believed to have been killed or died of overwork and starvation, and subsequent chaos.

Some of them, after spending most of their lives in the United States, are sent back to a homeland they hardly know after running afoul of U.S. law.

“They - their families, actually - fled the terrors of the Khmer Rouge era and post - Khmer Rouge chaos. Many were born in Thai refugee camps,” said Bill Herod, spokesman for the Khmer Vulnerability Aid Organisation (KVAO), a group that helps Cambodian deportees adjust after being sent back from the United States.

Cambodian Prime Minister Hun Sen has in the past criticized the United States over the deportations and accused it of breaking up the families of those forced to leave.

Thirty-five of the 37 deportees were convicted criminals who were sent back to Cambodia via a U.S. Immigration and Customs Enforcement (ICE) flight from Dallas, ICE said in a statement on its website.

ICE said it had increased the number of Cambodian immigrants it had deported from 2017 to 2018 by 279%. There are still about 1,900 Cambodians in the United States who are subject to deportation, of which 1,400 are convicted criminals, according to ICE.

“All of them have served time in prison for felony convictions. Some come directly from prison, but most completed their sentences long ago and were living freely at the time they were detained for deportation,” Herod said of the deportees who arrived on Thursday.

U.S. President Donald Trump’s administration has already deported thousands of people from Vietnam and Cambodia with criminal records as part of broader attempts to limit immigration to the United States.

The United States has been seeking to send thousands of immigrants from Vietnam back to the communist-ruled country despite a bilateral agreement that should protect most from deportation. [L3N1RN51W]

Trump has made illegal immigration a centerpiece of his administration and is highlighting the issue as he aims for re-election in 2020.