Thai police on Friday (Aug 28) said three Uighur Muslims, among dozens detained in the kingdom for illegal entry last year, have been questioned over the deadly Bangkok bombing.

Eleven days on from the bombing at Erawan shrine, which killed 20 people and wounded scores more, authorities are hunting for a prime suspect who police describe as a foreign man.

No arrests have been made, despite the circulation of grainy CCTV footage of the lead suspect.

Security analysts have speculated that China's ethnic Uighur minority - or their co-religious sympathisers - may have been behind the attack, motivated by Thailand's forced repatriation of more than 100 Uighur refugees last month to an uncertain fate in China.

"Police in (eastern) Sa Kaeo province have questioned three Uighurs," national police chief General Somyot Poompanmoung told reporters in Bangkok on Friday, without giving any further details.

Scores of suspected Uighurs - a Turkic-speaking minority in China's northwestern Xinjiang region who have long chafed under Chinese control - were sentenced for illegal entry in Thailand in March 2014.

Many were found to have entered the kingdom along its eastern border with Cambodia, with the biggest check point in Sa Kaeo province, as others were discovered during a raid on a suspected people-smuggling camp in the kingdom's deep south.

They presented themselves to police as Turkish and were held in detention as Thai authorities determined their nationalities, amid a bitter tussle between Turkey and China over where they should be moved.

Then in July, Thailand suddenly deported 109 Uighurs to China - a move widely condemned by rights groups and the US over fears for their safety - while an earlier group of 172 women and children were sent to Turkey.

At the time, the Thai government said around 50 Uighur Muslims remained in immigration detention facilities, as their nationalities were being confirmed.

A Thai police spokesman on Thursday refused to "exclude any possibility" when asked whether Turkish nationals in the country had been questioned over the Bangkok shrine bomb.

Uighurs in Xianjiang, who number around 10 million, have long accused China of cultural and religious repression. Scores have fled the restive region in recent years.

Others have stepped up a domestic campaign of violence - usually with knife assaults - but are not known to have ever carried out an attack outside China, or anything as sophisticated as the Erawan blast.

Thai police have so far issued one arrest warrant for the unidentified man suspected of the shrine bombing and a second for a man over a blast the following day near a popular tourist pier, which sent people scurrying but caused no injuries.