Leading Southern Baptist Albert Mohler has criticised therapies that attempt to turn people from gay to straight. Mohler said homosexuality cannot be turned on or off like a switch. But he continued to argue that gay behaviour is sinful and said only by turning to the Bible could it be addressed.

He was speaking at a press conference at the start of the Southern Baptist theological seminary's three-day conference, "Homosexuality - compassion, care and counsel for struggling people".

Mohler, president of the seminary, based in Louisville, Kentucky, restated his belief that marriage can be only between a man and a woman. He said gay people could become straight by accepting the Bible, but added that Christians had sinned against gays by "reducing a massive human struggle to simplistic explanations." Redemptive therapy did not have the same power as redemptive prayer, he said, in comments reported by AP. Kentucky is the state where Rowan County clerk Kim Davis went to jail for defying a federal court's orders to issue same-sex marriage licenses.

"In the case of many people struggling with this particular sin, we do not believe that some kind of superficial answer whereby they can turn a switch from being attracted to persons of the same sex to being attracted to persons of the opposite sex," he said.

"By God's grace, that might happen over time as a sign of God's work within the life of that individual. But ... for many, many people struggling with these patterns of sin, it will be a lifelong battle."

Gay rights protesters outside the conference called for prayers for love, inclusion and respect and held up placards that read: "Love Needs No Cure."

Mohler admitted that the traditional Christian view that marriage is between a man and a woman is "decidedly not what is heard in the larger secular culture." He said the conference was an opportunity for evangelicals to talk about "what this moral revolution will demand of us and how we can respond with the full wisdom of the Christian faith."

Derek Penwell, a minister who was among the protesters, said: "Any movement that takes as its organizing principle the fact that people are somehow defective is wrong and it's destructive. And it adds to the kind of abuse that a group of people have faced for too long."