The new Thai government has vowed to crack down on websites deemed insulting to the royal family, alarming campaigners who had hoped it might curb a recent surge in the use of lèse-majesté laws.

Cases involving the offence – which carries a sentence of up to 15 years in jail – have soared in the last five years. Thailand also blocked or suspended almost 75,000 sites between 2007 and 2010, mostly under computer crimes legislation in relation to lèse-majesté.

Campaigners hoped the new government would ease restrictions, particularly given the complaints filed against several leaders of the "red shirt" movement whose support brought Puea Thai to power. But following pressure from the ousted Democrats, deputy prime minister Chalerm Yubamrung pledged to set up a "war room" to deal with the issue online, the Bangkok Post reported. "Websites [guilty of lèse-majesté] will not be tolerated by this government. I will take action as quickly as possible," he said.

The issue's increasing sensitivity comes amid the ill health of the revered 83-year-old king and the bitter political conflict between Thai elites, such as the powerful military, and supporters of Thaksin Shinawatra, ousted as prime minister in a 2006 coup. His sister, Yingluck, now leads the country and Puea Thai is seen as his party.

David Streckfuss, the leading expert on the issue and author of Truth on Trial in Thailand, said 30 lèse-majesté charges were sent to the lower courts in 2006, 164 in 2009 and 478 in 2010. Multiple charges are often heard in single cases.

The lèse-majesté law says anyone who defames, insults or threatens the king, queen, heir apparent or regent should be punished with three to 15 years in prison, but does not define what constitutes such behaviour. "It has become conflated with any criticism of the institution," said Streckfuss, who drew a parallel with McCarthyism. "It's the easiest, most vague and ambiguous shot at people."

Earlier this month 22-year-old student blogger Norawase Yospiyasathien was charged. Other cases causing particular alarm include those of Somsak Jiamteerasakul, a historian who proposed reforms to the monarchy; Thai-born American citizen Joe Gordon, whose blog linked to a banned book on the king; and webmaster Chiranuch Premchaiporn, accused of not deleting user comments deemed to insult the king quickly enough.

Chiranuch's trial under the computer crimes act resumes next month, and police could yet act on a separate complaint under the lèse-majesté law. She faces up to 50 years in jail, though sentences are often reduced after conviction. "We can't deny any more that there is a problem," said Chiranuch, who runs the independent Prachathai news site. "There's strong evidence that, with the political conflict, this law has been abused."

Hundreds of scholars, lawyers, writers and activists have joined calls for reform of the law. They stress they are not questioning the monarchy, but the way the lèse-majesté provision has been used. "[People] are using it as a political tool to destroy their enemies," Worachet Pakeerut, a law professor at Thammasat University, told Associated Press last month.

Proposals include reducing the maximum sentence and allowing only an official royal body to register complaints. At present, anyone can; the royal family itself has never done so.

Some advocates of reform point to comments the king made in 2005, saying it would be "problematic" if people were unable to criticise him."I said [reform] would not be as easy as a change in the government," said Chiranuch. "It is quite clear the former government have put pressure on the new one by pushing them to promise not to amend the law."

Some believe Chalerm made the announcement so Puea Thai could concentrate on other priorities. Others hope the tough rhetoric might help it avoid tough action.

"It may be that Mr Chalerm was merely being overzealous in trying to assure the Puea Thai government's loyalty to the monarchy, but it is ironic because of the many accusations that the lèse-majesté law was used by the previous government to persecute some of the party's loyal supporters," the Bangkok Post noted in an editorial on Sunday.

"Brutal shutdown of lèse-majesté sites by the Yingluck administration is not the right way to win the heart and mind and protect the institution," warned the red-shirt-aligned Ratchaprasong News in a tweet.