Japan (search) on Tuesday warned it might sanctions against North Korea (search) after accusing the communist country of failing to properly investigate the fates of Japanese citizens it kidnapped years ago.

North Korea has admitted to kidnapping 13 Japanese in the 1970s and 1980s to train them in Japanese language and culture. The regime released five in 2002 but has said the eight others died — a claim many Japanese don't believe.

North Korea has pledged to investigate the alleged deaths and provide more proof to Japan, but a Japanese delegation that returned from Pyongyang on Monday after a third round of talks said the North Koreans had little new information to offer.

The negotiators returned with the alleged remains of one victim and documents and possessions of the seven others, but the lack of substantial progress triggered a string of calls for tougher measures against the reclusive regime.

"We are disappointed because there was no progress at all," Chief Cabinet Secretary Hiroyuki Hosoda told reporters Tuesday. When asked about sanctions, he said: "After we make a thorough analysis, we will look into what we'll do."

Asked about whether Japan still planned to send a second installment of food aid to North Korea as planned, Hosoda said, "I think it is one of the things we need to look into."

Japan shipped half of a pledged 250,000 tons of food — wheat, corn, soy beans and edible oil — to North Korea earlier this year and planned to sent the rest through the World Food Program and other international aid agencies before next April.

The aid was promised by Prime Minister Junichiro Koizumi (search) in May, when North Korean leader Kim Jong Il vowed to reinvestigate the whereabouts of the eight, plus two other unconfirmed kidnapping victims.

But the lack of concrete results have soured hopes of a resolution of the dispute, and Koizumi suggested late Monday that sanctions were possible. Two earlier rounds of talks in Beijing this summer also made little headway.