The perpetrators of last month's deadly Bangkok bombing were a network that trafficked Uighur Muslims and launched the attack in anger at Thailand's crackdown on the trade, police said on Tuesday.

No group has claimed responsibility for the Aug. 17 bombing at the Erawan Shrine that killed 20 people, an attack police chief Somyot Pumpanmuang ruled out as revenge for Thailand's forced repatriation in July of 109 Uighurs to China.

Thai official statements on the possible motive have been sketchy and Somyot did not say what evidence investigators were basing their latest assessment on.

"It's about a human trafficking network that has been destroyed," he told reporters.

"Deporting those 109 people, the Thai government did in accordance with international law. We also sent them to Turkey, not just China."

Police have poured water on speculation the bombers were international militants and have until now denied links to the Uighurs, who are mostly Muslim and say they flee China's western Xinjiang region due to persecution. Beijing rejects that.

The Uighur issue is sensitive for the Thai government and any link between the bombing and their deportation at China's behest could expose it to criticism that its foreign policy may have resulted in the blast.

Somyot said the Bangkok bomb and the ransacking of the Thai consulate in Istanbul - which occurred the day after the deportation - were "for the same reason: illegal human migration, with an origin here and destination Turkey."

"The cause of the bombing ... Simply speaking, we destroyed their operation and they are angry," he said.

The ransacking of the consulate was widely seen as a response to the deportation of the Uighurs.

Speculation of militancy linked to Uighurs was fuelled by the use by several suspects of Chinese passports, at least one with Xinjiang as birthplace.

Many Uighurs seek passage to Turkey via Thailand. Some Turks recognise a common cultural and religious bond with Uighurs.

Thai police issued an arrest warrant for a man using a Chinese passport who they say they last tracked to Turkey and played a role in planning the attack.

A Turkish official on Monday said there was no record of the man entering and Thailand had not notified Turkey about the suspect.

Thai police have come under criticism for not seeking outside help in their investigation.

The Bangkok Post newspaper said on Tuesday foreign cooperation was "not just desirable, but necessary".

"Still, authorities remain reluctant to openly seek the easily available aid and advice from other countries," it said.