The Ministry of Foreign Affairs has warned Thai tourists not to carry items for strangers after two Thai women were arrested at Tokyo's Narita airport on drugs charges earlier this week.
The arrests follow warnings issued by the Royal Thai Embassy in Tokyo two weeks ago telling Thais not to try to smuggle drugs into the country.
Ministry of Foreign Affairs spokeswoman Busadee Santipitaks said the women were arrested for allegedly possessing and trying to traffic cocaine into Japan.
If found guilty, they face up to 10 years in jail and a fine of up to 30 million yen (8.7 million baht). The two have not contacted the Thai embassy for help, though another 10 people have done so recently, taking the total number arrested, mainly for drug offences, to 16 since Nov 14.
The embassy on Nov 20 reposted warnings from 2014 and said Japanese police had reported the arrest of many Thais recently.
Before mid-November, 35 Thais had been arrested this year and had contacted the embassy in drug-related cases, Ms Busadee said, adding they were mainly women.
"This year, Thais arrested and who sought help from the embassy included 11 people accused of possession and smuggling drugs into Japan, and 15 people living in Japan who were jailed for drug possession," Ms Busadee said.
"There are likely Thais who were arrested but did not contact the embassy," she said.
Ms Busadee warned Thai tourists that they should not agree to carry anyone's belongings unless they know the owner and what the belongings contain.
Meanwhile, tour guides for trips to Japan voiced concern that Thais smuggling drugs were creating a negative perception of Thai tourists.
Thanakorn Jaisuksakuldee, a Thai-Japanese translator, wrote on Facebook on Tuesday that two Thai women on a group tour were arrested at Narita airport.
Japanese authorities have been keeping an eye on Thai tourists, he said in his post, shared among tour guides in Japan.
Another Facebook user who also works in Japan using the name Roongtonkit Prated wrote that Japanese authorities were subjecting Thai tourists to searches, while Thai tour guides had been questioned.
Since July 1, 2013, Thai nationals have been able to visit and stay in Japan for 15 days without having to apply for a visa.
A consular official at the Japanese embassy in Bangkok, who asked not to be named, said Japan does not currently have a plan to change its visa policy toward Thailand.