Virginia’s ban on equal marriage is unconstitutional and should no longer be defended, State Attorney General Mark Herring has concluded.

The Democrat on Thursday said the state will instead side with same-sex couples who are seeking to have the ban struck down.

He said: “As attorney general, I cannot and will not defend laws that violate Virginians’ rights. The commonwealth will be siding with the plaintiffs who have brought this case and with every other Virginia couple whose right to marry is being denied.”

Mr Herring said: “There have been times in some key landmark cases where Virginia was on the wrong side of history and the wrong side of the law, and as attorney general I’m going to make sure that the person representing the state’s legal position on behalf of the people of Virginia is on the right side of history and the right side of the law.”

He was referring to the case of Loving vs Virginia, in which the ban on interracial marriage was eventually struck down.

He will make the case that the ban on same-sex partners marrying violates the fourteenth amendment to the US constitution.

In a statement, Republican House Speaker William J. Howell said: “I am very concerned about his announcement today and the dangerous precedent it sets with regard to the rule of law. The Attorney General has a constitutional and statutory obligation to enforce and defend the duly adopted laws and Constitution of Virginia. This is not an obligation that can be taken lightly.

“The Attorney General’s decision today demonstrates a great deal of disregard for that obligation, as well as the legislative and democratic processes by which those laws are adopted.”

Legislation to overturn the ban was introduced earlier this month.

In the US, 17 states and the District of Columbia currently allow same-sex marriage, while 28 states still have constitutional bans in effect.

On Tuesday, Six same-sex couples in Florida filed a lawsuit to overturn the state’s ban on equal marriage.