Italian designers Dolce and Gabbana on Monday accused Elton John of being authoritarian, ignorant and hypocritical as a celebrity-driven row over IVF babies and gay adoption showed no sign of abating.

John, 67, stirred up a storm when he called for a boycott of the designer label in reaction to an interview in which Domenico Dolce referred to babies conceived through IVF as "synthetic".

In Instagram comments that have been endorsed by celebrities including Victoria Beckham, Ricky Martin, Sharon Stone, Courtney Love and Martina Navratilova, the gay star accused the Italian duo of "wagging your judgemental little fingers at IVF."

He added: "Your archaic thinking is out of step with the times, just like your fashions. I shall never wear Dolce and Gabbana ever again. #BoycottDolceGabbana."

The hashtag was the top trending one on Twitter in Britain on Monday and in the top three in Italy, with most posts highly critical of the Italian duo.

The designers, who are also gay and were in a long-term relationship with each other until 2005, claimed it was John who was being judgmental, not them.

I'm Sicilian

Dolce said his comment that IVF was not for him should not have been interpreted as disapproval of anyone else's choices.

"I'm Sicilian and I grew up in a traditional family, made up of a mother, a father and children," he said in a statement.

"This is the reality in which I grew up, but it does not imply that I don't understand different ones. I was talking about my personal view, without judging other people's choices and decisions."

His business partner Gabbana was so infuriated by John's statement that he posted the comments #fascist and #boycotteltonjohn on the singer's Instagram page before deleting them.

On Monday, he expressed more measured criticism.

"I didn't expect this, coming from someone whom I considered, and I stress 'considered', an intelligent person like Elton John.

"I mean, you preach understanding, tolerance and then you attack others?

"Only because someone has a different opinion? Is this a democratic or enlightened way of thinking? This is ignorance, because he ignores the fact that others might have a different opinion and that theirs is as worthy of respect as his.

"It's an authoritiarian way of seeing the world: agree with me or, if you don't, I'll attack you."

Fears for brand

John has two young sons with his husband David Furnish who were conceived through IVF and born thanks to a surrogacy arrangement.

In the original interview, in Italy's Panorama magazine, Gabbana said he would have a child tomorrow if he could, while Dolce explained why he did not feel he could go down that road.

"You are born and you have a father and a mother," Dolce said.

"Or at least that's the way it should be, and that's why I'm not convinced by children from chemistry, synthetic babies, uteruses for rent, semen chosen from a catalogue."

Victoria Beckham weighed into the row on Monday by tweeting: "Sending love to Elton David Zachary Elijah all the beautiful IVF babies."

Gay Latino star Ricky Martin, who has five-year-old twins, on Sunday accused the Italian duo of fuelling bigotry. "@dolcegabbana ur voices R 2powerful 2B spreading so much h8," he tweeted. "Wake up,Its 2015 Luv urselves guys #boycottdolcegabbana."

The fashion house has also come under fire from some gay activists in Italy and they received support they could probably have done without from right-wing politicians, one of whom accused John of behaving "like the Taliban."

The backlash is causing concern among D&G executives about the impact on the company's global brand and sales as hopes it would blow over quickly begin to look optimistic.