A US judge has ordered that a Kentucky official be jailed for contempt of court after she repeatedly refused to issue marriage licences to gay couples.
Kim Davis has said that her Christian faith should exempt her from signing the licences.
The US Supreme Court declared gay marriage legal in June.
After interviewing her fellow clerks, the judge said Ms Davis could go free if she allowed her deputies to grant the licences, but Davis refused.
Ms Davis, an elected official in Rowan County, has said the Supreme Court's ruling conflicts with her beliefs as a born-again Christian.
"You can't be separated from something that's in your heart in your soul," Ms Davis said. "I promised to love Him with all my heart, mind and soul because I wanted to make heaven my home."
US District Judge David Bunning said he had "no alternative" but to jail her, because issuing fines would not change her mind.
"Her good faith belief is simply not a viable defence," said Mr Bunning. "Mrs Davis took an oath. Oaths mean things."
He added that letting one person's beliefs supersede the authority of the court would be a dangerous example to set.
Ms Davis' lawyer, Mat Staver, said: "The judge said that he's going to bring her back out in another week and see if she's changed her mind. But knowing Kim Davis, she's a woman of strong conviction and conscience and I don't see her changing her mind."
Ms Davis' lawyer had claimed that her deputy clerks could only issues licenses under Davis' authority, but the judge overruled that objection.
Five deputy clerks told the judge on Thursday they would comply with the court order. A sixth deputy clerk, Ms Davis' son, Nathan, refused.
The judge decided not to hold Nathan Davis in contempt of court.
Hundreds of protesters lined up outside of the federal courthouse on Thursday, chanting and waving signs both of support and opposition.
Local reporters tweeted photos of the two different camps in close quarters outside of the courthouse.
Protesters screamed "Love won! Love won!" outside of the courthouse after learning of the decision.
Ms Davis stopped issuing marriage licenses to all couples in June after the legalisation of gay marriage, turning couples away repeatedly.
The US Supreme Court on Monday rejected the argument that her faith prevented her from carrying out her duty.
"I have no animosity toward anyone and harbour no ill will. To me this has never been a gay or lesbian issue. It is about marriage and God's word," she said in a statement.
She can only be removed from her position if the Kentucky legislature impeaches her, because she is an elected official.
Various 2016 Republican presidential candidates, like Mike Huckabee, Louisiana Governor Bobby Jindal, Senator Ted Cruz and Senator Marco Rubio, have come out in support of Ms Davis' decisions.
Others like Carly Fiorina, Senator Lindsey Graham and Ohio Governor John Kasich have said she must do her job and comply with the law.