SINGAPORE, Aug 21 (Reuters) - Singapore will decriminalise sex between men but has no plans to change the legal definition of marriage as being between a man and a woman, Prime Minister Lee Hsien Loong said on Sunday.

LGBTQ groups welcomed Lee's decision to repeal Section 377A of the penal code, a colonial-era law that criminalises sex between men, but also expressed concern that ruling out same-sex marriage would help to perpetuate discrimination.

In his annual national day rally speech, Lee said Singaporean society, especially young people in the city-state, were becoming more accepting of gay people.

"I believe this is the right thing to do, and something that most Singaporeans will now accept," he said.

It was unclear when exactly Section 377A would be repealed.

Singapore becomes the latest Asian country to move toward ending discrimination against members of the LGBTQ community.

In 2018, India's highest court scrapped a colonial-era ban on gay sex, while Thailand has recently edged closer to legalising same-sex unions.

Under Singapore's Section 377A, offenders can be jailed for up to two years under the law, but it is not currently actively enforced. There have been no known convictions for sex between consenting adult males for decades and the law does not include sex between women or other genders.

Lesbian, gay, bisexual, transgender, and queer (LGBTQ) groups have brought multiple legal challenges attempting to strike down the law, but none has succeeded.

On Sunday, several LGBTQ rights groups said in a joint statement they were "relieved" by Lee's announcement.

"For everyone who has experienced the kinds of bullying, rejection and harassment enabled by this law, repeal finally enables us to begin the process of healing. For those that long for a more equal and inclusive Singapore, repeal signifies that change is indeed possible," they said in the statement.

But the groups also urged the government not to heed calls from religious conservatives to enshrine the definition of marriage in the constitution, saying this would signal that LGBTQ+ citizens were not equal.