The French finance minister, Michel Sapin, has admitted to behaving inappropriately towards a female journalist, days after allegations of harassment forced the resignation of the vice-president of the lower house of parliament.

Sapin apologised for his behaviour while insisting that the incident, which has become known as “knickergate”, should not be “confused with the seriousness of harassment or sexual assault”.

He had been under pressure since the publication last month of a book about French politics that alleged that he had pinged the knicker elastic of a journalist as she bent down to pick up a pen at last year’s world economic forum at Davos.

The incident was also referred to, without naming Sapin, in a petition by 40 female journalists last year, demanding that the sexual harassment of female political journalists in France stop. The tribune, published by Libération, described a minister who, when seeing a journalist bend down to pick up a pen, “couldn’t restrain his hands” while murmuring: “Ah, but what are you showing me here?”

When the book, called L’Elysée Off, came out last month, Sapin’s office strenuously denied any such incident had taken place, saying the claims were “false and slanderous”. At a press conference on Tuesday, Sapin said the accusations against him were “in the realm of calumny” and “totally false”.

But on Wednesday morning, the minister backtracked and issued a statement to Reuters and AFP in which he said he was sorry.

“During a trip to Davos in January 2015, amid about 20 people, I made a comment to a journalist about her clothing and put my hand on her back,” Sapin said in the statement. “There was no aggressive or sexual intent in my conduct but the mere fact that the person was shocked shows that those words and this gesture were inappropriate, and I was, and still am, sorry,” he added.

Sapin, one of Socialist president François Hollande’s closest allies, said the journalist had at the time immediately asked to talk with him and expressed her “indignation”, and that he “sincerely apologised” to her.

He said that “the facts” of what happened “should not be confused with the seriousness of harassment or sexual assault”, adding: “I consider the fight against all forms of debasement, assault or brutality – of which women are too often the victims – is essential in our society and across the world.”

Sapin said that “in the current circumstances” he felt he had to issue the statement to clarify what happened. He had come under increasing pressure as female politicians, journalists and activists spoke out this week against ongoing and serious sexual harassment in French politics.

The resignation on Monday of the vice-president of the lower house of parliament, the Green MP Denis Baupin, who was accused of sexual harassment by women in his party, has sparked a new debate on the issue in France. Judges have opened a preliminary investigation into Baupin, who vehemently denies the allegations.

Hundreds of female French politicians and activists on Tuesday denounced sexual harassment in the corridors of power and what they called a Mafia-style code of silence that lets it go unpunished.

Several female politicians had referred to the Sapin case since Baupin stepped down. Delphine Batho, a Socialist MP and former minister, had said: “There is a minister who must explain himself or at least apologise.”

Sapin has described the allegations against Baupin as “appalling” but said it was up to the judiciary to establish the facts.