By Aukkarapon Niyomyat and Panarat Thepgumpanat
BANGKOK (Reuters) - Thai police are investigating 12 new complaints of royal defamation 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 stabilizing 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 offense.
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.
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.
Volunteers have appeared outside the palace, handing out free water and food as mourners line up in the heat and rain. Old folk have been waiting in the shade of awnings.
"If I could follow him I would but I don't know if I have enough good karma to meet him in death," said one old woman.
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 material.
Deputy Prime Minister Prachin Chanthong said the government had found up to 60 websites insulting the monarchy and threatening security.
The junta has asked internet service providers to block some of the sites and was seeking court orders to block other encrypted sites, he said, adding police had a team of about 100 people monitoring online content and would recruit more.
Justice Minister Paiboon Koomchaya said he had written to seven ambassadors to ask for help in prosecuting 19 lese majeste suspects living in their countries.
He did not identify the countries. He said earlier it was his duty to seek prosecutions even though he realized they would be difficult to achieve.
The junta has sought to reassure the public that a roadmap to democracy, with a general election in 2017, remains on course and there is no uncertainty over the succession which would happen after a period of mourning. It is not clear how long.
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.
A former prime minister, Thanin Kraivichien, 89, was made acting head of the Privy Council of royal advisers, after its previous head, Prem Tinsulanonda, stepped in as regent until Crown Prince Maha Vajiralongkorn ascends the throne.
(Additional reporting by Cod Satrusayang, Patpicha Tanakasempipat and Kaweewit Kaewjinda; Writing by Patpicha Tanakasempipat; Editing by Robert Birsel)