The incident was "spontaneous", and the migrant workers involved were employed by a variety of companies and lived in different places, Lee said in Tokyo.
Asked whether one of the possible causes of the riot was the eruption of pent-up tensions among foreign workers in Singapore, Lee said, "We have not seen any evidence of that. There is no tension, there is no sense of grievances or hardship or injustice."
The migrant workers involved in the rampage left 39 police and civil defence staff injured and 25 vehicles -- including 16 police cars -- damaged or burnt.
Singapore previously witnessed violence of such scale during race riots in 1969.
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"The riot happened spontaneously, it was localised. The people who were involved in the riot were not from one company, or one dorm (dormitory); they were from several dorms, many different companies, and it is unlikely that all the companies will have the same problem," The Sunday Times quoted Lee as saying.
Lee has ordered the formation of a special committee to probe the riot and warned to use "full force of the law" against trouble-makers.
A two-day ban on the sale and consumption of alcohol were imposed after the riot covering an area of 1.1 square kilometres in the Serangoon Road area, most of which covers Little India, which was the scene of the riot on December 8.
Even as authorities tighten the inflow of foreign workers over the years, Lee said their population needs to be managed, and there was an on-going inter-ministerial committee that looks into their welfare.
"One of the focuses was to try our best to see how we could speed up the construction of more dorms, so that the workers who are now housed in HDB estate or private properties, which have been rented out, they can be put in proper dorms. Then I think they can be better taken care of and there can be less impact on the community," Lee said