US Vice President Joe Biden has come back at criticism for his defence of same-sex marriage, saying he “could not remain silent any longer” on what he is now calling “the issue of our day.”

In a speech at Senator Tom Harkin’s annual Iowa steak-fry fundraiser on Sunday, Biden reiterated his support for marriage equality.

He said: “A lot of people criticised me for speaking out, not long ago, about gay marriage. I could not remain silent any longer. It’s the civil rights of our day. It’s the issue of our day.”

He was referring to a 2012 incident in which “Meet The Press” host David Gregory asked Biden whether he was “comfortable” with same-sex marriage.

Biden replied: “I am vice president of the United States of America. The president sets the policy. I am absolutely comfortable with the fact that men marrying men, women marrying women, and heterosexual men and women marrying another are entitled to the same exact rights, all the civil rights, all the civil liberties.

“And quite frankly, I don’t see much of a distinction — beyond that.”

Biden also publicly defended gay marriage only a week ago, at the 19th anniversary celebration of the Violence Against Women Act.

He said: “I make no apologies on the issue of marriage.”

In January earlier this year, Joe Biden swore in the first ever openly LGBT senator Tammy Baldwin.

As US President Barack Obama met with nine LGBT activists during his trip to St Petersburg for the G20 summit earlier this month, he said was so “energised intellectually and inspired” by their talks, the meeting lasted twice as long as expected.