Thai police have detained nine people suspected of hacking government websites to protest against amendments to a cyber security law that critics say strengthens the authorities' oversight of the internet.

Parliament passed legislation this month amending a cyber crime law, which rights groups said would likely to lead to more extensive online monitoring by the state.

In response, hackers launched a wave of cyber attacks last week, shutting down dozens of government websites.

The government said the websites were only down temporarily and the attacks caused minimum disruption.

Deputy Prime Minister Prawit Wongsuwan told reporters nine people had been arrested in connection with the hacking.

One of those arrested has been charged with breaking the cyber crime law, police said.

"The rest remain in custody and are being processed in accordance with the law," police spokesman Dejnarong Suthicharnbancha told Reuters.

Thailand's military government has increased online censorship since it seized power in a 2014 coup, in particular to block perceived insults to the royal family.

Criticism of the monarch, the regent or the heir is a crime known by the French term lese majeste, which carries a jail sentence of up to 15 years.

Since the death of King Bhumibol Adulyadej on Oct. 13 and the ascension of new King Maha Vajiralongkorn on Dec. 1, authorities have shut down hundreds of websites carrying what they consider to be material critical of the monarchy.

The military government is also sensitive about criticism of the 2014 coup, and a new constitution subsequently drawn up.

The government has promised to hold an election in 2017.