The US state of North Dakota has asked for a judge to dismiss a lawsuit challenging its ban on same-sex marriage.

Seven same-sex couples in the state filed the lawsuit in June in federal court,meaning there are now no states in the US with unchallenged same-sex marriage bans.

The office of the state attorney general filed a motion late on Tuesday which responded to the lawsuit.

“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,” solicitor general Doug Bahr argued in the 50-page response.

“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 continued.

He argued that the state is also not required to recognise the marriages of same-sex couples married 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.

Voters in North Dakota approved a ban on same-sex marriage back in 2004, with 73%.