SHANGHAI, June 22 -- Shanghai customs said Thursday that Chinese and Cambodian law enforcement authorities jointly seized 1.1 tons of cocaine and detained four drug trafficking suspects late last year.

It is the largest amount of cocaine seized in recent years, they said.

They said the case was not made public earlier because it was quite complicated and there were international drug traffickers involved.

In November last year, customs staff at Shanghai Yangshan Port were suspicious of a shipment marked as fish. The shipment had been sent from Ecuador, was transiting through Yangshan, and its destination was Sihanoukville, Cambodia.

Inspectors found 1,102 blocks of cocaine in the shipment, which was seized by customs under the instruction of China National Narcotics Control Committee.

On November 23 last year, a team jointly dispatched by the Ministry of Public Security, General Administration of Customs, and Shanghai local authorities, travelled to Cambodia.

Thanks to close cooperation between Chinese and Cambodian authorities, four suspects, two Vietnamese nationals, and two Vietnamese Canadians, were caught. Three others are still on the run, and are being tracked by Cambodian and Vietnamese law enforcement, Shanghai customs said.