State officials are asking a federal judge to dismiss a lawsuit challenging North Dakota's constitutional prohibition on same-sex marriage, despite a wave of court decisions striking down bans in other states.

The state attorney general's office filed the motion late Tuesday in U.S. District Court in Fargo. North Dakota Solicitor General Doug Bahr argues in court documents that states have the right to define and regulate marriage.

"Nothing in the United States Constitution prevents the people of North Dakota from defining marriage as the legal union between a man and a woman," Bahr wrote in his 50-page response.

North Dakota voters overwhelmingly approved a state constitutional ban on same-sex marriage 10 years ago. The ballot received 73 percent approval.

"The people of North Dakota, through the deliberative political process, retain the traditional understanding of marriage as the union between a man and a woman," Bahr wrote.

Similar cases are being heard in courtrooms around the country, and gay marriage bans have already been struck down in several other states, including on Tuesday in deeply conservative Kentucky. The fight to legalize gay marriage began in earnest after the U.S. Supreme Court struck down part of the federal Defense of Marriage Act last year. Since then, gay rights advocates have won 18 cases in federal and state courts.

North Dakota Attorney General Wayne Stenehjem on Wednesday said his office is duty bound to defend the ban, despite what appears to be a growing national tide in support of gay marriage.

"It is the constitutional duty of the attorney general to represent the state when it is sued," he said in a statement to The Associated Press.

"Only the Supreme Court can determine whether North Dakota's enactment is constitutional or not," he said.

North Dakota is the last state with a gay marriage ban to be sued by same-sex couples. The complaint, filed last month by Minneapolis attorney Josh Newville on behalf of seven couples, seeks a declaration that the ban is unconstitutional and asks that the state be forced to issue marriage licenses to same-sex couples and recognize gay marriages from other states. The lawsuit claims violations on three issues that are guaranteed in the 14th Amendment to the Constitution: equal protection, due process and right to travel.

Newville told the AP Wednesday that he's not surprised the state is defending the ban.

"It seems to me the defense of these bans has become more of a political thing at this point than (having) any legitimate legal basis," he said.

A second lawsuit challenging North Dakota's ban has since been filed in federal court by a Fargo couple legally married in Minnesota.

Bahr argues that the U.S. Constitution doesn't require North Dakota to recognize legal same-sex marriages in other states.

"The fact North Dakota's marriage laws are different from the marriage laws of some other states does not establish a viable claim that the challenged provisions violate the right to interstate travel," he wrote.