HELENA, Mont. (AP) – Four gay couples are suing Montana over its constitutional ban on same-sex marriage.

SIOUX FALLS, S.D. –  Six couples filed a federal lawsuit Thursday seeking to block South Dakota’s gay marriage ban, leaving North Dakota as the only state in the country with an unchallenged law prohibiting same-sex weddings.

State marriage bans have been falling around the country since the U.S. Supreme Court last year struck down part of the federal Defense of Marriage Act.

THOMPSON, N.D. (AP) – An eastern North Dakota mayor is joining other municipal leaders around the country in supporting same-sex marriage, becoming the first mayor in the state to formally join the effort.

Thompson Mayor Karyn Hippen says she’s proud to be the 400th member to join Mayors for the Freedom to Marry, a coalition of same-sex marriage supporting mayors organized by an advocacy group.

Thompson says she has a 23-year-old son who is gay and wants to see him get married someday.