A human rights campaigner said he thought the Archbishop of Canterbury's view on gay marriage is "evolving" after a private meeting to discuss the issue.
Peter Tatchell was invited to meet the Most Rev Justin Welby after branding the new Archbishop's stance against same-sex marriage as "homophobic".
They held an hour-long meeting in Lambeth Palace, where Mr Tatchell claims the Archbishop indicated his support for civil partnerships for same-sex couples, but seemed "fearful" of expressing his views on gay marriage publicly.
Lambeth Palace said it was a "private" conversation and that they would not comment further.
But after the meeting, Mr Tatchell said: "It was a very frank discussion with some considerable areas of disagreement. Overall I found Justin Welby very willing to listen. The meeting was constructive - it was in his opinion the beginning of a dialogue which he plans to continue with myself and other gay campaigners. He continually described same-sex relationships as different and continued to describe them as intrinsically different."
He said the Archbishop did not give him a "moral justification" about why "that difference justified discrimination in law".
Mr Tatchell said: "Justin Welby said that he is in favour of legal provision to recognise same-sex marriages but that he is unhappy with the current Bill. He said he was open to further consideration about how same-sex relationships should have legal recognition and rights although he tended to take the view that gay relationships were different and therefore should be acknowledged within legislative framework from marriage.
"The sticking point was Justin Welby's view that same-sex relationships are in his view an intrinsically different kind of relationship from heterosexual marriage and therefore he felt very uncertain and unconvinced that marriage was appropriate as a legal framework. He didn't give a convincing explanation other than the fact that they are just different. I'm hopeful that it will in time lead to some reform of the Church's opposition to gay marriage."
The meeting was offered by the Archbishop after Mr Tatchell wrote an open letter on March 20. The Archbishop thanked Mr Tatchell for his "very thoughtful" letter and said he made "powerful" points.
Mr Welby was officially enthroned as Archbishop of Canterbury last month.