CINCINNATI - A federal judge Monday ordered Ohio authorities to recognize gay marriages on death certificates, saying the state's ban on such unions is unconstitutional and that states cannot discriminate against same-sex couples simply because some voters don't like homosexuality.

Although Judge Timothy Black's ruling applies only to death certificates, his statements about Ohio's gay-marriage ban are sweeping, unequivocal, and are expected to incite further litigation challenging the law. Ohio's attorney general said the state will appeal.

Black cited the Supreme Court's June decision striking down part of a federal anti-gay-marriage law, saying that the lower courts are now tasked with applying that ruling.

"And the question presented is whether a state can do what the federal government cannot - i.e., discriminate against same-sex couples ... simply because the majority of the voters don't like homosexuality (or at least didn't in 2004)," Black said in reference to the year Ohio's gay-marriage ban passed. "Under the Constitution of the United States, the answer is no."

Eighteen states and the District of Columbia allow same-sex weddings, up from six before the Supreme Court decision.

Black wrote that "once you get married lawfully in one state, another state cannot summarily take your marriage away," saying the right to remain married is recognized as a fundamental liberty in the U.S. Constitution.

"When a state effectively terminates the marriage of a same-sex couple married in another jurisdiction, it intrudes into the realm of private marital, family, and intimate relations specifically protected by the Supreme Court," he wrote.

Black's decision stems from a lawsuit in July by two gay Ohio men whose spouses recently died and wanted to be recognized on their death certificates as married. The two couples got married in other states.