Hong Kong  - Japan has said sorry for planting cannabis on an incoming Hong Kong passenger to test out one of its sniffer dogs, a news report said Wednesday.

Embarrassed officials had to issue a public appeal to the passenger to return the 142 grams of cannabis after the sniffer dog failed to detect it and the customs officer forgot which bag he planted the drugs in.

The incident on Sunday in which a passenger on a Cathay Pacific flight into Tokyo was targeted as he collected his suitcase from the airport carousel brought an outcry from the Hong Kong government and tourism officials.

The drugs - worth almost 10,000 US dollars - were eventually recovered on Monday evening from the passenger in a Tokyo hotel but it is not known if the passenger was traced or whether he or she alerted officials.

In a statement to Wednesday's South China Morning Post, a spokesperson for Japan's customs authorities said the department felt "great regret and we offer our deepest apologies."

The statement went on: "We will also thoroughly investigate the case and punish concerned officers to ensure a repeat of such an incident will not occur."

The 38-year-old customs officer responsible told reporters that he realized he should not have planted cannabis on an unsuspecting passenger but said he had done it before and the dogs had always previously found the drugs. (dpa)