BANGKOK (Reuters) - Twenty ethnic Uighur Muslims from China broke out of a detention center near the Thai-Malaysia border, Thai officials said on Monday, after digging holes in the wall and using blankets as ladders.

The 20 were part of the last remaining group of more than 200 Uighurs who were detained in 2014.

Members of the group identified themselves as Turkish citizens and asked to be sent to Turkey but more than 100 were forcibly returned to China in July 2015, a move that sparked international condemnation, including from rights groups who feared they could face torture in China.

Hundreds of people have died in recent years in China’s troubled far western region of Xinjiang due to violence between majority Han Chinese and Uighurs, who speak a Turkic language.

Over the years, hundreds, possibly thousands, of Uighurs have escaped unrest in Xinjiang by traveling clandestinely via Southeast Asia to Turkey.

Twenty-five Uighurs dug through their cell wall using broken tiles and then used blankets to climb out of the cell to make their dramatic escape from the detention center in Thailand’s southern Songkhla province, immigration officials said.

Five were caught but the rest fled, officials said.

“Twenty are still at large,” Police Captain Prasit Timmakarn, sub-inspector of the detention center, told Reuters, adding: “Heavy rain helped to mask the loud escape noises.”

Prasit said authorities have set up checkpoints along the border.

In August 2015, a bomb planted at Bangkok’s Erawan shrine killed 20 people, most of them foreign tourists. Thai police arrested two Uighur men who are still on trial.

Authorities said the attack was prompted by an earlier crackdown on human smuggling networks but many analysts and diplomats said it was likely an act of revenge for Thailand’s deportation to China of the more than 100 Uighurs.

The Chinese government has blamed much of the Xinjiang unrest on separatist Islamist militants, though rights groups and exiles say that anger over tightening Chinese controls on the religion and culture of Uighurs is more to blame.

China routinely denies any repression in Xinjiang.