India's home ministry urged the country's Supreme Court on Thursday to reverse a landmark decision to decriminalise gay sex, saying homosexuality was immoral, "against nature and spreads HIV."

The Supreme Court is hearing more than a dozen petitions filed to overturn a 2009 ruling by a Delhi High Court that made gay sex between consenting adults legal for the first time.

The colonial-era ban was judged to be unconstitutional in a decision hailed by gay activists as a victory in their fight for equal rights and opportunities in the world's biggest democracy.

Gay sex ‘is highly immoral and against the social order,’ additional solicitor general P.P. Malhotra, who is representing the home ministry, told the top court.

He added that it was ‘against nature and spreads HIV.’

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The ministry said it favoured the ban staying in place in order to prevent child abuse and because Indian society was largely against homosexuality according to a survey by the Law Commission, Malhotra explained.

"Laws can't run separately from society and the morals of the time," he said.