There is no reason to believe the riot in Little India was due to unhappiness among foreign workers here, Prime Minister Lee Hsien Loong said on Saturday.
Last Sunday's incident was "spontaneous", and the migrant workers involved were employed by a variety of companies and lived in different places, he told reporters in an interview in Tokyo, where he was attending a summit celebrating the 40th anniversary of Asean-Japan relations.
Asked for his comments on talk that one of the possible causes of the riot was the eruption of pent-up tensions among foreign workers in Singapore, PM Lee said: "We have not seen any evidence of that.
"The riot happened spontaneously, it was localised.
"The people who were involved in the riot were not from one company, or one dorm; (they were from) several dorms, many different companies, and it is unlikely that all the companies will have the same problem."
Mr Lee added there were also some signs that alcohol was a factor.
About 400 people, mostly foreign workers of South Asian origin, were involved in the melee. Thirty-three Indian nationals have been charged in court so far.