The Canadian prime minister, Justin Trudeau, has for the first time publicly acknowledged that he apologised in 2000 to a reporter who alleged he groped her, but said he was very confident he did not act inappropriately.

The accusation first appeared in a local newspaper a few days after a music festival in British Columbia that Trudeau, then a 28-year-old teacher, was attending.

The unsigned editorial in the Creston Valley Advance accused Trudeau of “groping” and “inappropriately handling” an unnamed reporter who was covering the event.

While the editorial offered no specifics on what had happened, it claimed the reporter felt “blatantly disrespected” and Trudeau had apologised for his behaviour. “I’m sorry,” the editorial alleged Trudeau to have said. “If I had known you were reporting for a national paper, I never would have been so forward.”

The festival had raised thousands of dollars to support avalanche safety, a cause Trudeau had become involved with after his brother Michel died in an avalanche in 1998.

The allegation has dominated political discussion in Canada in recent days after it was highlighted by a political commentator last month.

The reporter behind the allegation – who is also believed to be the author of the editorial – has not responded to interview requests from the Guardian.

Trudeau addressed the allegation briefly on Monday, describing the day of the event as a “good day” and one in which he did not recall any “negative interactions”.

After calls for an independent investigation into the claim and opposition criticism of his initial response, Trudeau addressed the issue at length on Thursday.

“I’ve been reflecting very carefully on what I remember from that incident almost 20 years ago,” he told reporters. “I do not feel that I acted inappropriately in any way. But I respect the fact that someone else might have experienced that differently.”

When asked about why he had apologised to the woman after the alleged incident, Trudeau said: “If I apologised later, it would be because I sensed that she was not entirely comfortable with the interaction that we had.”

Pressed further, he acknowledged he had atoned for his actions at the time. “I apologised in the moment,” he said, without giving details.

Trudeau said he had not attempted to contact the woman, nor had anyone from his team. “We don’t think that would be appropriate at all.”

He said the issues surrounding sexual assault and other behaviours had been something he had been actively engaged in since his early 20s. He characterised the allegation against him as part of an “awakening” currently taking place in society.

“I don’t want to speak for her, I don’t want to presume how she feels now,” Trudeau said. “I’m responsible for my side of the interaction, which certainly – as I said – I don’t feel was in anyway untoward.”

He continued: “But at the same time, this lesson that we are learning – and I’ll be blunt about it – often a man experiences an interaction as being benign, or not inappropriate, and a woman, particularly in a professional context can experience it differently. And we have to respect that, and reflect on it.”