Virginia Governor Ralph Northam has apologised after his 1984 student yearbook page emerged, showing a photo featuring men in racist costumes.
"I am deeply sorry for the decision I made to appear as I did in this photo and for the hurt that decision caused then and now," he said in a statement.
Black politicians in Virginia called the image "disgusting" and Republicans urged the Democrat to resign.
The picture showed a man in blackface and another man in Ku Klux Klan robes.
It appeared on a page with other photos of Mr Northam, who was aged about 25 at the time, as well as personal details about him.
He did not elaborate on which costume he was wearing, but said he appeared in a photograph that was "clearly racist and offensive".
Mr Northam was elected governor of Virginia in November 2017.
How has this come about?
Mr Northam's yearbook page, which came from the paediatric neurologist's time at Eastern Virginia Medical School, was first published by conservative website Big League Politics.
The Virginian-Pilot newspaper tweeted a picture of the page which it said it obtained from the medical school library.
BREAKING: Gov. Ralph Northam yearbook page shows blackface and Klan photohttps://t.co/6A89ejp5Ho— The Virginian-Pilot (@virginianpilot) February 1, 2019
An official from the medical school verified the photo and told the Huffington Post it came from a "student-produced publication".
The page, which features Mr Northam's full name and photos of the future doctor and politician, also included a quote from a Willie Nelson song that read: "There are more old drunks than old doctors in this world so I think I'll have another beer."
What has Northam said?
"This behaviour is not in keeping with who I am today and the values I have fought for throughout my career in the military, in medicine, and in public service," the governor said in a statement after the image was made public.
"But I want to be clear, I understand how this decision shakes Virginians' faith in that commitment."
He continued: "I recognise that it will take time and serious effort to heal the damage this conduct has caused. I am ready to do that important work.
"The first step is to offer my sincerest apology and to state my absolute commitment to living up to the expectations Virginians set for me when they elected me to be their governor."
Mr Northam later released a video statement via Twitter in which he said he was "deeply sorry" for the offence the image had caused.
"I accept responsibility for my past actions and I am ready to do the hard work of regaining your trust," he said.
Before he was elected governor, Mr Northam served for a decade as a Virginia state legislator.
His responsibilities as governor include implementing state laws, restoring voting rights for individuals who have had them withdrawn and issuing pardons.
What is the reaction?
The Virginia Legislative Black Caucus, which comprises African Americans elected to the Virginia General Assembly, said it was "still processing what we have seen about the governor" but described the images as "disgusting, reprehensible and offensive".
"These pictures rip off the scabs of an excruciatingly painful history and are a piercing reminder of this nation's sins. Those who would excuse the pictures are just as culpable," it said in a statement.
The photo also prompted a swift backlash from conservatives, including Jack Wilson, the chairman of the Republican Party of Virginia, who called on Mr Northam to step down.
"Racism has no place in Virginia," he said in a statement. "These pictures are wholly inappropriate. If Governor Northam appeared in blackface or dressed in a KKK robe, he should resign immediately."
Calls for his resignation also came from four Democratic candidates for president - Senators Kirsten Gillibrand, Kamala Harris and Cory Booker, and Texan mayor Julian Castro.
These images arouse centuries of anger, anguish, and racist violence and they’ve eroded all confidence in Gov. Northam’s ability to lead. We should expect more from our elected officials. He should resign.— Cory Booker (@CoryBooker) February 2, 2019
Democratic Senator Elizabeth Warren, who is considering a presidential run in 2020, also called for Mr Northam to resign.
These racist images are deeply disturbing. Hatred and discrimination have no place in our country and must not be tolerated, especially from our leaders – Republican or Democrat. Northam must resign.— Elizabeth Warren (@ewarren) February 2, 2019
The Ku Klux Klan is one of the oldest and most infamous hate groups in the US, and has targeted African Americans, Jews, Catholics and immigrants, according to the Southern Poverty Law Center, which tracks hate groups.
The group has a long history, with KKK membership peaking in the 1920s.