A human rights group criticised Malaysia on Tuesday for sending a group of ethnic Uighurs back to China and urged an end to such deportations over fears of mistreatment and even torture.

The UN refugee agency also said it had sought access to the 11 people deported on August 18 as well as five others still in custody in Malaysia but had been denied by Malaysian authorities.

A senior Malaysian police official defended the government's actions in comments to AFP, saying the Chinese nationals, all members of the Uighur ethnic minority, were involved in a human-smuggling syndicate.

"This group has nothing to do with any political group or asylum-seekers. They are all involved in people smuggling," he said.

Announcing the deportations on Saturday, police said they had busted a Chinese people smuggling ring which was falsely trying to claim UN refugee status for its victims after smuggling them into Malaysia.

But New York-based Human Rights Watch denounced the deportations and urged they be halted, saying Uighurs faced "grave risk of torture" in China.

It also called on China to make known where the 11 deportees were.

"The treatment of these Uighurs is a litmus test for Malaysia’s commitment to basic principles of refugee protection," it said in a statement.

Many Uighurs, a Turkic-speaking and predominantly Muslim minority in China's remote northwestern Xinjiang region, allege decades of political and religious repression by China.

Their anger -- and China's resulting tight security in the region -- has triggered sporadic bouts of unrest.

The deportations come amid a refugee swap arrangement between Malaysia and Australia, which has been put on hold by a Canberra court.

Rights groups moved to block the deal, citing concerns over Malaysia's record on handling refugees.

United Nations High Commissioner for Refugees spokeswoman Yante Ismail said the agency had sought access to all 16 Uighurs. She said the five in detention had all previously applied for refugee status with the agency.

"We very much regret that the 11 individuals were deported without the opportunity for us to have access to them," she said in a statement.

The police official said there were no immediate plans to deport the five but that they could face criminal charges over fake Malaysian passports found on them.

The US-based Uyghur American Association called the deportations a "flagrant violation of international law" by Malaysia.

"(The deportations) follow an extremely disturbing trend of Uighurs deported from countries with strong trade and diplomatic ties to China," it said in a statement.

Human Rights Watch said other countries such as Thailand and Pakistan had recently deported Uighurs back to China, adding that it revealed "the bullying hand of China".