Updated

Thai police said Tuesday that they were stepping up security along the country's borders as they searched for around 20 suspected ethnic Uighurs who escaped an immigration detention center.

Local media published surveillance camera footage of the Monday escape in which the group climbed out of the detention center using two holes they seemingly made in a wall. They apparently used blankets to lower themselves down before running toward the detention center's exit.

Cherngron Rimpadee, an immigration police deputy spokesman, said police were patrolling the border between Thailand and Malaysia. Security in Malaysia was also tightened as the detention center was close to the border.

Cherngron said that the group had been detained since 2014 for illegally entering Thailand, but that police have not been able to identify their nationality.

"Our officials found them, so we have held them in custody to prepare to send them back," Cherngron said. "But there are still problems about proving their nationality."

In 2015, Thailand deported 109 ethnic Uighur refugees back to China, where they fled from, sparking criticism from the U.N. refugee agency, the United States and others.

Cherngron said he did not know whether Chinese officials had asked for this group of suspected Uighurs to be sent back to China. "It is an international relations concern that I don't know about," he said.

The Uighurs are a Turkic-speaking Muslim minority in far western China's Xinjiang region. The group has complained of harsh cultural and religious suppression as well as economic marginalization under Chinese rule.

China's position is that the Uighurs who were sent back by Thailand had left the country illegally. Beijing has accused Uighur separatists of terrorism in Xinjiang, where ethnic violence has left hundreds of people dead over the past two years.

In 2015, a bomb blast near a popular Hindu shrine in Bangkok killed about 20 people and Thai police blamed the attack on Chinese Uighurs.

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This story has been corrected to show that Thai police were patrolling the border between Thailand and Malaysia, not Myanmar, and that security in Malaysia, not Myanmar, was also tightened.