Miss Universe Thailand has renounced her title over remarks she made on social media, including one that "red shirt" activists, supporters of ousted prime minister Yingluck Shinawatra, should all be executed.

Last month's military coup was the latest convulsion in a decade-long conflict between the Bangkok-based royalist establishment and the rural-based supporters of Yingluck and her brother, former prime minister Thaksin Shinawatra.

Weluree Ditsayabut, 22, was crowned Miss Universe Thailand last month but comments she made months earlier soon surfaced, including one on her Facebook account referring to the red shirts which said: "I am so angry at all these evil activists. They should all be executed."

A tearful Ms Ditsayabut told reporters that she could not handle the vitriol directed at her on Twitter and Facebook.

"I felt under pressure," she said.

"I tried to improve myself but what I could not stand was to see my mother stressed.

"I have decided to sacrifice my status as Miss Universe Thailand."

The beauty queen also hit back at comments on her looks.

"Actually I'm fat, you animal!" read one post on her Twitter account, which has since been deleted.

It was unclear whether first runner up Pimbongkod Chankaew would replace Ms Weluree as Thailand's representative at the global competition, Miss Universe 2014.

'Return Happiness to Thailand'

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Meanwhile, a ballad penned by a coup-making army chief promising to bring happiness back to Thailand has been viewed more than 200,000 times on YouTube, in the military's latest effort to put a positive spin on its putsch.

The normally stern-faced General Prayuth Chan-ocha, who led the May 22 military overthrow of the civilian government, can now list songwriting among his talents after writing the lyrics to "Return Happiness to Thailand".

The song - featuring reassuring lines such as "we offer to take care and protect you with our hearts" and "give us a little more time" - has proved an hit since the Royal Thai Army band put General Prayuth's words to music on Friday and released it on their website.

By Monday, one uploaded video on YouTube had garnered 150,000 views, while other media sources posted links to the patriotic song that generated tens of thousands more hits.

"He (Prayuth) called me to see him for an hour. He wrote it with his own handwriting," said Colonel Krisada Sarika, head of the Royal Thai Army band.

"He wants a song which expresses his feeling for the people... he wants a song which Thai people listen to and then begin to love each other again."

Thailand's military has gone to great lengths to put some gloss on its latest coup, holding concerts with dancing soldiers and free food for bystanders.

General Prayuth, who is giving weekly televised addresses to the nation, has said he was forced to act after months of protest caused policy paralysis and saw nearly 30 people die in political violence.

Since seizing power from an elected government on May 22, the army has banned public protests, censored the media and summoned hundreds of politicians, activists and academics for questioning.

The nation has been torn apart since 2006 when the army ousted divisive billionaire Thaksin Shinawatra as premier.

Thaksin and his affiliated parties have won the electoral loyalty of the northern portion of the country with populist policies aimed at improving the lot of the rural poor.

But he is loathed by the Bangkok-based establishment - and its supporters in the military - who accuse him of destabilising Thailand through vote-buying, corruption and crony capitalism.

Thousands of people gave the general's song a "thumbs up" on YouTube while others posted comments supportive of the coup.

But General Prayuth's ditty was not universally popular.

"Returning happiness for one group -- while bullying the other group," said one angry YouTube comment.

"You should try to have an election and ask the people what they want."

Reuters/AFP