The Tokyo Metropolitan Police Department and Tokyo Customs' Haneda branch arrested the group on suspicion of importing or possessing the drug for profit in violation of Japan's Narcotics and Psychotropics Control Act, the Sankei Shimbun reported.

According to the newspaper, customs officers found cocaine under the insoles of a man and a woman who arrived on a flight from Kuala Lumpur International Airport on Oct. 9. The pair said they had come sightseeing with friends, and officers then searched three more people and found cocaine hidden the same way.

Each suspect carried about 1 kg, with 500 g under each insole, and officers first grew suspicious because one traveler wore shoes with unnaturally thick soles, Fuji News Network reported.

Hussein Omar Khan, head of the Malaysian police's Narcotics Criminal Investigation Department, said on Oct. 14 that the five, two men and three women, were among six Malaysians aged 19 to 26 who flew out of Kuala Lumpur International Airport's Terminal 2 on Oct. 9, Bernama reported. The sixth person returned to Malaysia.

A 24-year-old man among the five detained told investigators that a contact on Telegram offered a job carrying illegal drugs overseas for RM8,000 ($1,960) per person.

He was arrested along with his wife and friends, all among the five detained, and said he felt reassured after being told that people at the airport had been paid and he would not be checked, Fuji News Network reported.

Police believe all five may have been instructed to carry the drug into Japan and suspect an international smuggling ring is involved, the broadcaster said.

Travelers at Haneda Airport in Tokyo. Photo by Unsplash/Kazuo Ota

In Malaysia, Home Minister Saifuddin Nasution Ismail said on Oct. 13 his ministry was seeking details from Japanese authorities, including how the group allegedly passed security checks at Kuala Lumpur International Airport, and that he had told the police Narcotics Criminal Investigation Department to contact them, the New Straits Times reported.

Saifuddin said Tokyo was not on the government's original list of "hotspot" destinations, whose passengers face 100% screening including head-to-toe pat-downs and baggage checks.

"I believe the narcotics division will provide an immediate report on the circumstances surrounding this incident," he said.

Hussein said his department would send a team to Japan to investigate the arrests and any links to drug syndicates in Malaysia and abroad, Bernama reported.