BANGKOK: Thai police are investigating 12 new complaints of royal defamation found on social media lodged since the death of King Bhumibol Adulyadej last week, a sharp rise amid intensifying scrutiny of anything deemed offensive to the monarchy.

The death last Thursday of the revered king, who was 88, after seven decades on the throne has plunged the Southeast Asian country into mourning and heightened sensitivity about the monarchy.

King Bhumibol was seen as a stabilising figure in a country often racked by political turmoil.

Prime Minister Prayuth Chan-ocha has moved quickly to quash any uncertainty around the royal succession, saying Crown Prince Maha Vajiralongkorn would ascend the throne after a period of mourning that he had requested.

Insulting the monarch, the regent or the heir, known by the French-language term "lese-majeste", is a crime in Thailand that carries a jail sentence of up to 15 years for each case.

Police spokesman Kitsana Pattanacharoen said there had been 12 lese-majeste cases since last Thursday, with arrest warrants issued for eight suspects and four already in police custody.

"Their crime was posting messages or pictures which insulted the monarchy on social media," he told Reuters.

There were 70 cases in the two-and-a-half years from a May 2014 coup up to last Thursday, said Weerawat Somnuek, a researcher at Thai legal monitoring group iLaw.

"Twelve cases in a week is a lot," Weerawat told Reuters.

GRIEF, ANGER

The stepped-up prosecutions come at a time of deep grief among Thais, who have for decades seen the late king as a unifying father figure.

People are dressing in black around the country, and have been streaming to Bangkok's gilded Grand Palace to pay their respects to the late king, who is lying there.

No date has been set for a royal cremation but it is expected to take place in about a year.

The Thai stock market, which fell sharply last week as investors worried about stability after King Bhumibol, has been stable this week.

But some grief-stricken people have been quick to anger.

In some cases, violence has erupted against individuals deemed disrespectful, while similar anger has erupted online against people whose posts have been seen as inappropriate.

Thailand's main mobile telecoms operators have, at the government's request, asked customers to report websites and social media posts deemed inappropriate or insulting.

The government also asked internet service providers to monitor content and inform platforms such as Facebook, Twitter and Youtube to block offensive content. Failure to do so would be considered a crime, the government said.

The junta has sought to reassure the public that a roadmap to the restoration of democracy, which promises a general election in 2017, remains on course and there is no uncertainty around royal succession.

Prime Minister Prayuth told reporters after a cabinet meeting on Tuesday that the roadmap was unchanged and the succession would happen after a period of mourning.

"There are a lot of preparations needed to be made before succession," junta spokesman Colonel Winthai Suvaree told Reuters.

Winthai said an estimate the prime minister gave on Tuesday of seven to 15 days was meant only to convey a passage of time and was not to be taken literally.

"The length of time he mentioned were just a turn of phrase and not exact figures," Winthai said.

The formal procedure for the prince becoming king involves the cabinet informing the president of the legislature. The assembly then invites the prince to ascend the throne.

Pornpet Vichitcholcha, president of the National Legislative Assembly, told reporters that the legislature was ready to handle the matter at any time.