(CNN) The mother of detained teen blogger Amos Yee has written a heartfelt apology letter to her son, as he faces years in "reformative training" after being jailed for a Youtube video where he criticized Singapore's founding politician.

"Sorry for not teaching you well... Mummy is wrong," wrote Mary Toh in a widely-shared Facebook post yesterday. "Sorry for telling you that you are in the safest country. You are feeling so insecure and scared now."

"Sorry for urging you to be a law-abiding citizen. The laws are doing you more harm than good now," the note continued. "Sorry for encouraging you to be creative and expressive. You are regarded as crazy and rebellious instead."

In March, Yee, then an unknown 16-year-old blogger, was arrested after publishing a Youtube video praising the death of Singapore's first prime minister, Lee Kuan Yew and comparing him unfavorably to Jesus.

He had also posted an image showing two cartoon figures having sex, with Lee and former British prime minister Margaret Thatcher's faces digitally added.

Days later, Yee was arrested and charged with violating Singapore's obscenity laws, and for "wounding religious feelings" with his remarks. Found guilty in May, he is currently detained at a mental hospital while undergoing court-ordered psychiatric examinations, the Straits Times reported.

Depending on the examination's results, Yee could be required to undergo more than two years of mandatory psychiatric treatment in lieu of prison time.

Yee has also faced threats from Singaporeans who are furious over his video.

In April, Yee was slapped by a 49-year-old man outside a courtroom -- that man was sentenced to three weeks in jail for his assault.

Yee has also been the target of multiple rape threats from Internet users, said activist blog The Online Citizen

To support her son, Toh has attended court hearings wearing a T-shirt reading "#FreeAmosYee," said the Straits Times

Advocates demand Yee's release

In a statement Tuesday, Hong Kong pro-democracy group Scholarism, led by student leader Joshua Wong, called for Yee's immediate release.

"The fact that the Singaporean government has forcibly imprisoned a teenager... undeniably reflects the unreasonable oppression and the very limited acceptance of dynamic voices in the so-called 'modernised' society of Singapore," it said in a Facebook post

The group held a protest outside the Singapore consulate in downtown Hong Kong Tuesday in support of Yee.

Phil Robertson, the deputy Asia director of Human Rights Watch, also demanded Yee's release, citing Singapore's 1995 ratification of the UN Convention on the Rights of the Child, which guarantees children's rights to free speech.

"Nothing that Amos Yee said or posted should ever have been considered criminal -- much less merit incarceration," he said in a statement

"The dismal state of Singapore's respect for free expression can be seen in the decision to impose the criminal justice system on outspoken 16-year-olds."