A mother and her boyfriend have been arrested for allegedly locking a toddler inside a washing machine in Thailand.

The 'love-crazed' mum, 25, and her new partner, 27, were detained by police on July 17 over their alleged mistreatment of her daughter, 2, at their home in Bangkok.

The arrest came when the pair posted photos online showing them locking the hapless girl inside a washing machine. They captioned the pictures 'This is what bad girls deserve'.

Police superintendent Police Colonel Lertsak Kheamsap from the Tha Kham district said: 'We have summoned the couple and subjected them to drug tests, which came back negative. The child is now under the temporary care of the Ministry of Social Development and Human Security.'

The child's grandmother, who reported the alleged abuse, said she was alarmed upon finding various bruises on the girl. She said: 'I've raised my grandchild since she was little, and she never had bruises like these before.'

She said the girl's real father had died from electrocution around three months ago and she suspected the mum's new lover was behind the alleged beatings.

She said: 'My daughter loves this man so much that she sometimes ignores her own children, and even lets her new husband put the child in the washing machine and post it online.'

The unnamed mum initially claimed her daughter incurred the injuries while at the local nursery. But staff denied her claims and said the girl had not been involved in any accidents.

They said the youngster had been enrolled with them since June 15, and would arrive with bruises and 'fracture wounds' on her ear.

They said she would cry frantically whenever her stepdad came to fetch her, and seemingly look to them for help.

Speaking to officers, the stepfather, who works as a taxi driver, allegedly admitted to hitting the girl 'due to her naughty behaviour', but said he 'did not do it violently.'

He also said they had placed the child inside the washing machine 'as a joke'.

Police Colonel Lertsak said: 'The couple have been charged with causing bodily harm and domestic violence.'