Canada's PM Justin Trudeau has said he cannot remember how often he wore blackface as a younger man, as a scandal deepened ahead of an election.
He was speaking after more images of him wearing black make-up when he was younger emerged.
"I am wary of being definitive about this because of the recent pictures that came out, I had not remembered," he told reporters in Winnipeg.
The revelations have rattled his campaign in a tight election race.
Canadians will go to the polls on 21 October.
The images are so embarrassing for the prime minister because he has positioned himself as a champion of social justice, inclusivity and diversity.
When his cabinet was sworn in in 2015, half the appointments were women; three were Sikhs and two members were from indigenous communities.
What are the latest images?
A video came to light on Thursday in which he is seen in a white T-shirt and torn jeans, his face and limbs covered in black make-up.
In the footage, shot in the 1990s, he is seen laughing, throwing his hands in the air, sticking his tongue out and pulling faces.
Mr Trudeau would have been in his late teens or early 20s at the time.
Blackface, which was more prevalent in the past, particularly in the entertainment industry, involves white people painting their faces darker - and is widely condemned as a racist caricature.
What about the other episodes?
On Wednesday, the embattled PM apologised for wearing brownface make-up at a gala at a private Vancouver school where he taught nearly two decades ago.
A 2001 yearbook picture obtained by Time Magazine shows Mr Trudeau, then aged 29, with skin-darkening make-up on his face and hands, at the West Point Grey Academy.
Mr Trudeau dressed up in the photo in an Aladdin costume.
Another photo has emerged showing Mr Trudeau, then a high school student, performing in a talent show, again wearing blackface. He was singing Day-O, a Jamaican folk song popularised by American civil rights activist Harry Belafonte.
How did Trudeau respond?
In Winnipeg on Thursday, the prime minister made his second appearance before reporters since the scandal broke.
He said: "Darkening your face, regardless of the context or the circumstances, is always unacceptable because of the racist history of blackface.
"I should have understood that then and I never should have done it."
Mr Trudeau said he had let a lot of people down. "I come to reflect on that and ask for forgiveness."
He said that failing to realise how hurtful his actions were could have resulted from "a massive blind spot" due to his privileged background.
Mr Trudeau has also been phoning Liberal candidates to apologise for his conduct.
What reaction has there been?
Defence Minister Harjit Sajjan, interviewed by the Canadian Broadcasting Corporation (CBC), said what Mr Trudeau did was wrong but pointed to his policies on promoting diversity.
Liberal MP Omar Alghabra told CBC his "heart sank" at the images.
"He's been a champion to combat against the type of pain this picture is causing," he said.
The leader of the opposition Conservatives, Andrew Scheer, speaking on Thursday, dismissed Mr Trudeau's apology as "not real".
"He was specifically asked if there were other instances where he engaged in this type of racist behaviour and he indicated that there was only one other incident and now we know there are at least three."
New Democratic Party leader Jagmeet Singh, a Sikh, said on Wednesday that the image was "troubling" and "insulting".
Residents of Toronto approached by the BBC seemed fairly unfazed by controversy.
"I really don't think it's a big deal," one woman said.
But another woman was disappointed: "At the same time I recognise that many of us, especially we white people, have to take a hard look at the things we have done in our past that are racist."
One man said: "It's an awful long time ago. Maybe just look at what he does now instead of what he did when he was in his 20s."
But one Ottawa resident, when asked if she found the images offensive, said: "I do."
Mustafa Farooq, executive director of the National Council of Canadian Muslims, said: "Seeing the prime minister in brownface/blackface is deeply saddening. The wearing of blackface/brownface is reprehensible, and hearkens back to a history of racism and an Orientalist mythology which is unacceptable."
The images have brought a strong response in Canadian media.
The photos undermine perceptions of who Mr Trudeau "really is", a Canadian Broadcasting Corporation commentator says.