Hong Kong police said Thursday they had arrested nearly 1,200 people in raids on illegal gambling dens and brothels during a month-long crackdown on triad activities.

Police also seized about 40 kilograms (88 pounds) of ketamine and contraband goods in the operation nicknamed "Thunderbolt 2012" concluded last week, a police spokesman told AFP.

"Police raided 1,680 premises and questioned 28,437 individuals," he said, adding that the 1,191 people detained include 505 women.

The operation was jointly conducted with mainland Chinese and Macau police.

Hong Kong police said earlier this month that they had detained 130 suspected triad members for money laundering and running illicit gambling dens, seizing HK$3.4 million ($440,000) in local and foreign currencies.

Macau police have also mounted a similar operation, raiding casinos, hotels and arrested 150 people which came after a spate of murders in the city that have raised fears of a return to the gaming hub's violent past.