Prime Minister Yingluck Shinawatra's lawyer yesterday lodged a complaint with Dusit police, alleging a Thai-language newspaper cartoonist defamed her.
Norawich Lalaeng, the lawyer, also accused Thai Rath cartoonist Somchai Katanyutanan, 72, better known as "Chai Ratchawat", of making public his defamatory messages and violating the Computer Crime Act by posting them on his Facebook page.
Mr Somchai posted on his personal page his opinions about Prime Minister Yingluck Shinawatra's controversial speech delivered in Mongolia this week.
Along with the opinions, he wrote a message saying: "Please understand prostitutes are not evil women. Prostitutes just sell their body but an evil woman sells the nation."
The message ran along with a picture of Ms Yingluck taken with Mongolian president Tsakhiagiin Elbegdorj.
Ms Yingluck told a democracy conference in Mongolia on Monday that anti-democratic regime elements still exist in Thailand.
She said the 2006 coup had derailed democracy in Thailand and overthrown the government of her brother Thaksin who was the elected premier at the time.
Ms Yingluck also criticised independent organisations set up by the military-backed 2007 constitution. She said the organisations abused their authority against the will of the people.
A group of female Pheu Thai MPs, meanwhile, blasted Mr Somchai for not being a "gentleman" and petitioned the Thai Journalists Association to look into the defamation matter. They also said they were consulting the party's legal team about bringing legal action against the cartoonist.
List MP Sunee Luangwijit said the prime minister was telling the truth when she mentioned the 2006 coup and its consequences during her speech in Mongolia.
Ms Yingluck's speech had not damaged the country but instead had shown the international community that Thailand and its government now aimed to ensure democracy in the country, Ms Sunee said.
Mr Somchai's remarks reflected his derogatory views about women, she said.
Jarupan Kuldilok, another Pheu Thai list-MP, said her group would translate its statement that denounced Mr Somchai's behaviour into English and forward it to international human rights groups and Mongolia.
In Chiang Mai, a group of local red shirts known as the Rak Chiang Mai 51 Group gathered outside Thai Rath's news centre in the province condemning Mr Somchai for the comments which they strongly believed referred to Ms Yingluck.