Media playback is unsupported on your device Media caption Singapore's National Library Board says it will not change its decision, as Sharanjit Leyl reports

Singapore authorities have withdrawn from libraries two children's books featuring same-sex couples, sparking controversy amid a debate on gay rights in the conservative city-state.

And Tango Makes Three features a pair of gay penguins while The White Swan Express mentions a lesbian couple.

Petitions for the books to be put back have garnered thousands of signatures.

Gay sex is illegal in Singapore, and a recent gay rally drew an unprecedented backlash from religious groups.

The two books were removed earlier this week after a library user wrote into the National Library Board expressing concern about the books' content.

The library board said in a statement that it takes "a pro-family and cautious approach in identifying titles for our young visitors", and plans to pulp the books despite vocal opposition.

Nearly 5,000 people have signed an open letter and a petition calling for the books to be put back, arguing that the ban amounts to censorship and that the books are not against family values.

And Tango Makes Three is based on a real-life story of two male penguins which hatched an egg at the New York Zoo.

It has been the subject of intense controversy in the United States, and has consistently made it to the American Library Association's list of books which receive the most number of removal requests.

The White Swan Express features several would-be parents looking to adopt children in China, including a lesbian couple and a single mother.

Image copyright AFP Image caption The annual Pink Dot rally sees supporters forming the eponymous dot in downtown Singapore

The debate on gay rights has gathered steam in Singapore in recent years. The annual Pink Dot gay rally last month was met with a counter "pro-family" campaign backed by religious groups.

Gay rights proponents have launched two constitutional challenges to overturn a law that bans gay sex.

Singapore's government has said that while it will retain the law to reflect mainstream society's stand on the issue, it will not be actively enforced.