Rights groups have condemned a new law issued by Thailand's military-led government that gives the country's soldiers police powers, warning it could lead to troops committing human rights abuses.

Human Rights Watch, Amnesty International, and the International Commission of Jurists were among six groups that released a joint statement on Tuesday calling for the legislation to be rescinded.

On March 29, the country's armed forces, including paramilitary units, were given wide-ranging powers to detain suspects without arrest warrants for up to a week for several crimes.

The military said a crackdown on "mafia figures" was needed because of the lack of police officers to do the job.

But the rights groups said the move was a judicial power grab that would give troops immunity from prosecution and may lead to abusive acts such as torture and enforced disappearances.

They see it as part of a government campaign to stifle dissent and activism since military leaders seized power two years ago.

"Instead of paving the way for a return to democratic rule, the Thai junta has broadened its powers to do almost anything it wants, including committing abuses with total impunity," Brad Adams, Asia Director at Human Rights Watch, said in the statement.

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"Repression becomes a daily reality as Thailand descends further into military dictatorship.”

Champa Patel, Interim Director of Amnesty International's South East Asia and Pacific Regional Office, also warned of the absence of judicial oversight in the law.

"The order is yet another example of the pernicious removal of powers from the judicial system to review the military’s actions, to the detriment of rights protection and the rule of law," he said.

Wilder Tayler, Secretary General of the International Commission of Jurists, said the law would "certainly lead to violations of Thailand's international human rights obligations.

“We have observed a steady erosion of human rights protections in Thailand since the military coup of May 22, 2014 and this order signifies another jarring movement in the same direction,” he said.