Japanese customs officials apologized Monday for putting cannabis in an unsuspecting passenger's luggage but no one has come forward yet to accept the apology or to return the drugs.

A customs agent hoping to test Narita airport's sniffer dogs put 142 grams of cannabis into the side pocket of a randomly selected suitcase, officials said.

"The dog couldn't find it and the officer [then] forgot which bag he put it into," a spokeswoman told journalists in Tokyo. "If by some chance passengers find it in their suitcase, we're asking them to return it."

The cannabis is worth about $10,000 in Japan, which has some of the strictest anti-narcotics laws in Asia. No one has brought it back yet.

The head of customs at Narita apologized "deeply" for the incident.

"This case is deeply regrettable," Manpei Tanaka said.

Officials said the unnamed 38-year-old customs officer who planted the drugs was acting against regulations, which require a more controlled environment to test the airport's drug detecting dogs.

"I knew that using passengers' bags is prohibited," the officer was quoted as saying by the customs spokeswoman, "but I did it because I wanted to improve the sniffer dog's abilities.

"The dogs have always been able to find it before."

The man has been reprimanded and there is no word on the fate of the pooch that failed to find the drugs.