The American Civil Liberties Union has sued Rowan County Clerk Kim Davis on the behalf of two gay couples and two straight couples. Photo:

The American Civil Liberties Union has sued Rowan County Clerk Kim Davis on the behalf of two gay couples and two straight couples. Photo:

Updated: 10:00 p.m. EDT

LOUISVILLE, Ky. — A federal judge in Kentucky struck down the state’s ban on gay marriage on Tuesday, though the ruling was temporarily put on hold and it was not immediately clear when same-sex couples could be issued marriage licenses.

U.S. District Judge John G. Heyburn in Louisville concluded that the state’s prohibition on same-sex couples being wed violates the Equal Protection Clause of the U.S. Constitution by treating gay couples differently than straight couples. The ruling was the latest in a string of victories for gay marriage advocates across the nation, and marked the most recent conservative state to have its ban overturned.

Heyburn previously struck down Kentucky’s ban on recognizing same-sex marriages from other states and countries, but he put the implementation of that ruling on hold. That decision did not deal with whether Kentucky would have to issue marriage licenses to same-sex couples. Instead, Tuesday’s ruling dealt directly with that question.

“Sometimes, by upholding equal rights for a few, courts necessarily must require others to forebear some prior conduct or restrain some personal instinct,” Heyburn wrote. “Here, that would not seem to be the case. Assuring equal protection for same-sex couples does not diminish the freedom of others to any degree.”

Heyburn noted that every federal court to consider a same-sex marriage ban has found it unconstitutional. Gay rights activists have won 18 cases in federal and state courts since the U.S. Supreme Court in June 2013 overturned a key portion of the 1996 Defense of Marriage Act, allowing married same-sex couples to receive the same federal benefits as heterosexual couples. Only Judge Paul J. Kelly Jr. of the 10th Circuit Court of Appeals in Denver has argued for keeping a state ban on same-sex marriages.

A total of 13 gay marriage cases are pending in state and federal appeals courts. Those rulings all are on hold pending appellate court decisions.

Also on Tuesday, six couples sued to overturn Colorado’s gay marriage ban, a move that comes as the Republican attorney general urged Boulder officials to stop issuing marriage licenses to same-sex couples.

Elsewhere, the 7th Circuit Court of Appeals in Chicago ordered Indiana to recognize the marriage of a lesbian couple, one of whom is terminally ill, on an emergency basis.

The U.S. 6th Circuit Court of Appeals has scheduled arguments on rulings from Ohio, Michigan, Kentucky and Tennessee in a single session, on Aug. 6. Although the cases are unique, each deals with whether statewide gay marriage bans violate the Constitution. The Michigan case also dealt with a ban on state-issued marriage licenses to same-sex couples.