The Foreign Ministry has revoked Thaksin Shinawatra's Thai passports and police are looking to file lese majeste and other charges against him.
The ministry announced the decision in a statement on Wednesday.
Police believed one of his media interviews recently violated the lese majeste law, as well as other criminal and computer-crime laws.
The statement said security officials had asked the ministry to take action now that the Royal Thai Police Office had found the content of his interview undermined "national security and dignity".
"Police are investigating and preparing to take criminal action against him under Sections 112, 326 and 328 of the Criminal Code and Section 14 (3) (5) of the Computer Crime Act," it said.
As a result, the ministry revoked both Thaksin's Thai passports — No. U957441 and Z530117 — effective May 26, 2015.
Section 112 provides: "Whoever, defames, insults or threatens the King, the Queen, the Heir-apparent or the Regent, shall be punished with imprisonment of 3-15 years".
Sections 326 and 328 involve defamation, with imprisonment not exceeding two years and a fine not exceeding 20,000 baht.
Section 14 of the Computer Crime Act involves importing and disseminating computer data involving such offences. The penalty is imprisonment for not more than five years or a fine of not more than 100,000 baht, or both.
Thaksin's passports were previously revoked shortly after the 2007 coup, but when his sister Yingluck formed a government in 2011 they were reinstated to him.
The statement does not say which of his interviews police found offensive but the former prime minister told Choson Media in Seoul last Wednesday some groups were behind the May 22, 2014 coup.
In 2008, Thaksin was sentenced in absentia to two years in jail by the Supreme Court for Holders of Political Positions for abuse of power in sale of state land to his then wife when he was prime minister. He fled Thailand before he was sentenced and has since lived in self-exile abroad.
