LOUISVILLE, Ky. (AP) -- A federal judge in Kentucky struck down the state's ban on gay marriage on Tuesday, though the ruling was put on hold pending appeals and it was not immediately clear when same-sex couples could be issued marriage licenses.
The ruling was the latest in a string of victories for gay marriage advocates across the nation.
> RELATED: Read below to get an update on gay marriage rulings across the U.S.
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.
Kentucky Gov. Steve Beshear said the state will appeal.
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. The U.S. 6th Circuit Court of Appeals in Cincinnati has scheduled arguments on similar rulings from Kentucky, Ohio, Michigan and Tennessee in a single session on Aug. 6.
"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 struck down the federal Defense of Marriage Act. During that time, 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 lead plaintiff in the Kentucky case, Timothy Love, 55, of Louisville, said he was "ecstatic" about the decision and hopes to be able to marry his partner of 34 years, Larry Ysunza, once all the appeals are complete.
"We wanted to see the entire ban struck down," Love said. "Now, the headline is `Love Wins.'"
Dan Canon, one of the attorneys for the plaintiffs, said he was excited about the ruling because the day will arrive soon when same-sex couples can get a marriage license in Kentucky.
"We believe the opinion forcefully lays to rest any notion that Kentucky's anti-marriage laws are based on anything other than discrimination against homosexuals," Canon said.
In support of the ban, Beshear argued in part that Kentucky's prohibition encouraged, promoted and supported relationships among people who have the "natural ability to procreate." A stable birth rate ensures the state's long-term economic stability, Beshear argued in court records.
Heyburn, an appointee of President George H.W. Bush, dismissed the governor's argument because excluding same-sex couples from marriage does not change the number of heterosexual couples who choose to marry and have children.
"These arguments are not those of serious people," Heyburn wrote.
Martin Cothran, a senior policy analyst with the Family Foundation of Kentucky, said Heyburn "has declared martial law on marriage policy" in Kentucky.
"By taking another important area of policy out of the hands of voters, liberal judges have struck another blow against the separation of powers that is an underlying principle of our form of government," Cothran said.
Evan Wolfson, founder of Freedom to Marry, a group backing same-sex marriage, said the ruling shows the public is ready to remove the legal bans put in place in many states.
"It is wrong for the government to deny same-sex couples the freedom to marry the person they love; a freedom that is part of every American's liberty and pursuit of happiness," Wolfson said.
Gay marriage is legal in 19 states and the District of Columbia.
After Tuesday's ruling, expectations are higher than ever that the U.S. Supreme Court eventually will decide gays can marry in every state.
Here are some key things to know about the gay marriage movement and where it's headed:
WHERE HAVE JUDGES OVERTURNED BANS AGAINST GAY MARRIAGE?
Besides Kentucky, federal and state judges have ruled against bans in Arkansas, Colorado, Idaho, Kansas, Michigan, New Mexico,
Oklahoma, Oregon, Pennsylvania, Texas, Utah, Virginia, Wisconsin, Wyoming and Indiana. They have ordered Indiana, Kentucky, Ohio and Tennessee to recognize same-sex marriages from other states.
WHAT TRIGGERED THE SERIES OF PRO-GAY MARRIAGE DECISIONS?
The Supreme Court last year found that the 1996 Defense of Marriage Act that forbade the federal government from recognizing same-sex marriage improperly deprived gay couples of due process. That ruling came as polls showed a majority of Americans now support gay marriage.
Lower-court judges have repeatedly cited that Supreme Court decision when striking down same-sex marriage bans.
WHEN DOES THE ISSUE RETURN TO THE SUPREME COURT?
Legal experts say the Supreme Court eventually will take a gay marriage case after one or more appeals court rulings, but that won't happen until 2015 at the earliest. And the high court is under no obligation to take up the issue.
In any of the appellate cases, the losing party can appeal directly to the Supreme Court, or first ask for the entire appellate court to review the ruling.
It's unclear which case would reach the high court first. The Supreme Court also could hold off and see how the nation's appellate courts rule. It often waits until there is a conflict between appellate courts before taking a case.