A U.S. federal judge on Sunday ruled that the state of Alaska's ban on same-sex marriage was unconstitutional.

Judge Timothy Burgess of the U.S. District Court for Alaska made the ruling after hearing oral arguments on Friday challenging the state's 16-year-old ban.

"The Court finds that Alaska's ban on same-sex marriage and refusal to recognize same-sex marriages lawfully entered in other states is unconstitutional as a deprivation of basic due process and equal protection principles under the Fourteenth Amendment of the U.S. Constitution," Burgess wrote.

He also barred Alaska from refusing to acknowledge lawful same-sex marriages conducted in other states.

Five couples, four of whom already had legally married in other states and a fifth wishing to marry in Alaska, filed their suit against the state in May challenging the ban.

In 1998, Alaska voters enacted a constitutional amendment that excludes same-sex couples from marriage.

The state contended that the voters should have the final word, not the courts.