The Thai royal family was less than impressed by quirky emoticon-style illustrations used to satirise them. The emojis were used briefly in an instant text messaging service in the country before they were pulled.

Thailand's royal family is protected by some of the world's strictest lèse-majesté rules. Penalties can be extremely harsh, with insults costing several years in prison, particularly since the 2014 military coup.

The tiny illustrations popped up briefly on the popular Japan-based LINE instant messaging service, a police spokesman told Reuters. "We are investigating where the stickers came from and who did this," said Colonel Somporn Daengdee, deputy chief of the police's Technology Crime Suppression Division.

LINE allows users to create their own digital stickers and sell them online. Many users include the cartoon-like stickers in their messages.

The emojis do not appear to be particularly offensive, but it is unusual for Thais to see the royal family depicted so informally. Those familiar with stories about royal family members would likely spot representations of the crown prince who loved his late poodle, Air Chief Marshal Foo Foo (that was actually the dog's name), or his sister Princess Maha Chakri Sirindhorn, who is known for contributing arts and craft work to the community.

LINE, which is one of Thailand's most popular social media platforms, apologised for the set of images and said it was no longer available to purchase. The stickers had spread quickly online.

"LINE Corporation is aware of the culturally sensitive sticker set that may have caused discomfort among our users in Thailand," the company said in a statement posted online. "The sticker set in question has been pulled from the LINE Sticker Shop.

The stickers that users create and upload are checked by the head office in Japan but not in Thailand, a source told Reuters.

A group contacted Mashable, claiming they had created the stickers, but their claim could not be verified. The group said their work was a political message.

"In Thailand, reverence for the royal family has sometimes been exploited to silence political debate," members said in a statement. "We wanted to create some light-hearted stickers that show the Thai royals as just like any other family. The furious reaction of Thai police shows Thailand is still far from democracy and freedom of speech."