Former US Vice President Dick Cheney says he’s “surprised” that Mary Cheney, his lesbian daughter, vented her fury at older sister Liz’s opposition to equal marriage on Facebook.

Last month, Liz Cheney, a candidate for the US Senate seat of Wyoming, said she believed in the “traditional” definition of marriage.

The remarks prompted sister Mary Cheney to post on Facebook: “You’re just wrong.”

“Liz – this isn’t just an issue on which we disagree – you’re just wrong – and on the wrong side of history,” she wrote after watching her sister state her views on Fox News.

Mary Cheney posted a quote from her wife, Heather Poe, saying that the elder Cheney sister “didn’t hesitate to tell us how happy she was for us” when they wed last year in Washington DC.

“Liz has been a guest in our home, has spent time and shared holidays with our children,” Ms Poe wrote. “To have her now say she doesn’t support our right to marry is offensive to say the least.”

“We were surprised that there was an attack launched against Liz on Facebook, and wished it hadn’t happened,” Dick Cheney said at the National Press Club on Monday. “It’s always been dealt with within the context of the family and frankly that’s our preference.”

Yesterday, Mr Cheney tried to draw a line over the matter. Promoting a new book about his lifelong struggle with heart-related ailments, he said it was “obviously a difficult thing for a family,” but declined to comment further.

“That’s as far as I’m going to go on the subject,” Mr Cheney told his interviewer. “Don’t waste your time.”

Mary Cheney condemned her older sister in September for not supporting marriage rights for same-sex couples.

Dick Cheney himself said in 2011 “he didn’t have any problem with” same-sex marriage.