Issuing the order, Defence Minister Prawit Wongsuwon said that surveillance had begun earlier after the two visitor groups were found involved in passport forgery.
Immigration police and other security agencies were monitoring the aliens, the minister was quoted as saying by the Bangkok Post.
"We have two theories. They may have snuck into Thailand to have their fake passports done so that they can travel to another country. Or they may have arrived for terror attacks," Gen Prawit said.
The two suspects, however, denied the charges.
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