Four same-sex couples have been allowed to marry in St Louis, Missouri, despite the state constitutionally banning same-sex marriage.

The move, which was confirmed by St Louis Mayor Francis Slay on Thursday, is a direct challenge to the state’s authority to regulate marriage.

It follows the lead of a clerk in Boulder County, Colorado, who decided to ignore the state’s marriage ban and issue licenses to 34 gay couples.

Slay admitted he expected the move to trigger legal action, saying: “St. Louis is a city that doesn’t tolerate discrimination.

“We are sending a message on what’s right, and I can’t think of anything more right than this.

“I felt that if we didn’t do these things, and we didn’t do this here in St. Louis, it wouldn’t be done anywhere else in the state of Missouri.”

The couples were married by St Louis Recorder of Deeds Sharon Carpenter, to commemorate one year since the federal Defence of Marriage Act was struck down.

Carpenter said: “For years I contemplated taking this action, but the the legal climate was never right to take action and take a stand.

“However, that all changed with the United States Supreme Court decision to rule all citizens have the right to marry under the law.”

Couple of 39 years Richard Eaton and John Durnell were first to marry, followed by Tod Martin and David Gray, Miranda Duschack and Mima Davis, and Bruce Yampolsky and Terry Garrett.

Despite the official marriage documents from the city, the validity of the marriages is likely to be strongly disputed.

The state’s Attorney General Chris Koster has signalled his intent to prevent recognition of the marriages.

He said: “While I personally support the goal of marriage equality, my duty as Attorney General is to defend the laws of the state of Missouri.

“While many people in Missouri have changed their minds regarding marriage equality, Missourians have yet to change their constitution.”