George Takei with partner
George Takei and husband Brad Altman (L) were married in 2008, and are campaigners for sexual equality in the USDanny Molosho/Reuters

Star Trek star and gay rights activist George Takei has publically apologised after calling an African-American US Supreme Court Justice Clarence Thomas as a "clown in blackface".

In the interview with Fox 10 Pheonix Takei said, "He [Clarence Thomas] is a clown in blackface sitting on the Supreme Court. He gets me that angry. He doesn't belong there."

Takei's outburst followed Thomas' dissent verdict which he wrote when the US Supreme Court ruled five-to four-ruling in favour of equal marriage in the US.

Thomas said that same-sex marriage in the US was unconstitutional, because denying gays and lesbians the right to marry does not deny them of their dignity.

"Human dignity cannot be taken away by the government," wrote Thomas, who is black. "Slaves did not lose their dignity, any more than they lost their humanity, because the government allowed them to be enslaved. Those held in internment camps did not lose their dignity because the government confined them."

As a child Takei, a Japanese-American, was held in an internment camp during World War II along with his family. He described his experience in an article for MSNBC.com.

After Takei's interview was broadcast, he was widely criticised on social media for being racist.

Takei defended his comments in a statement on Facebook, saying that they were not racially motivated.

"I recently was asked by a reporter about Justice Clarence Thomas's dissent in the marriage equality cases... I was still seething, and I referred to him as a 'clown in blackface' to suggest that he had abdicated and abandoned his heritage. This was not intended to be racist, but rather to evoke a history of racism in the theatrical arts. While I continue to vehemently disagree with Justice Thomas, the words I chose, said in the heat of anger, were not carefully considered."

Blackface was makeup worn by white theatrical performers to appear black and was commonly used in the mid-19th century and the early 20th century. It was most famously used worn by the jazz musician Al Johnson and the Black and White Minstrels. It is now regarded as perpetuating racist stereotypes.

Takei married his long-time partner Brad Altman in 2008 and is a campaigner for sexual equality in the US.