Singaporean Amos Yee has been freed after a United States immigration appeals board upheld his application for asylum, saying his fear of persecution was "well-founded".

In a Facebook post at around 7am on Wednesday (Sept 27) Singapore time, he said: "Amos Yee is now a free man!"

A United States immigration appeals board has upheld Mr Yee's application for asylum, saying his fear of persecution was "well-founded".

Mr Yee's lawyer Sandra Grossman said on Tuesday (Sept 26) that the United States Board of Immigration Appeals had dismissed the Department of Homeland Security's appeal opposing an immigration judge's earlier decision to grant Mr Yee, 18, asylum.

The three-member board, in a written decision dated Sept 21, said it agreed with the immigration judge that Mr Yee's prosecution "was a pretext" to silence his political opinions.

It also agreed with the judge that "the cumulative harm in this case rose to the level of persecution", and that this "entitles the applicant to a presumption of a well-founded fear, that has not been rebutted".

Mr Yee had left Singapore for Chicago last December, a day before he was to report for a medical examination ahead of enlistment into national service, and sought political asylum in the United States.

The blogger, made headlines when he was charged in Singapore in 2015 for engaging in hate speech against Christians in a video he posted on YouTube, and for publishing an obscene image of former prime minister Lee Kuan Yew. He was convicted and given a four-week jail sentence.

Last year, he was charged again for hate speech, having deliberately posted comments on the Internet - in videos and blog posts - that were derogatory of Christianity and Islam. He pleaded guilty and was sentenced to six weeks' imprisonment and a $2,000 fine.

Mr Yee has been in US Immigration and Customs Enforcement detention since he arrived in the US and applied for asylum last December.

Chicago immigration judge Samuel Cole granted him asylum in March, saying he had been persecuted for his political opinions.

Singapore's Ministry of Home Affairs responded to the judge's decision with a statement outlining the obscenity-laden quotes that Mr Yee disseminated and got into trouble for, saying the US "allows such hate speech under the rubric of freedom of speech".

In April, the Department of Homeland Security (DHS) appealed the ruling, arguing that Judge Cole made errors of fact and law. The DHS had opposed Mr Yee's asylum application, saying the Singapore Government legitimately prosecuted Mr Yee.

Grossman Law and DHS subsequently submitted written arguments to the board in May.

The board, in upholding Judge Cole's decision, noted that he had "relied on severe mistreatment of the applicant, including being imprisoned with only adults and being placed in a mental institution with difficult conditions".

Grossman Law said the case will now be remanded to the Immigration Court in Chicago to allow DHS the opportunity to complete or update any pending security investigations or examinations.

"While a date has not been set for entry of the final order, it is likely to be soon, especially given the amount of time Mr Yee has been detained at US taxpayer expense," it added.

"The possibility also remains for a DHS appeal, though this is unlikely given the board's unambiguous decision."