The new head of scandal-hit UNAids has vowed to transform the agency’s culture to safeguard staff not only from sexual harassment – which she called “the tip of the iceberg” – but any abuse of power by those at the top.

Winnie Byanyima said she would draw on lessons learned following allegations of sexual misconduct at Oxfam, of which she was international executive director until earlier this year, to address problems at the UN agency.

UNAids was lacerated by an independent panel last December over “a work culture of fear, lack of trust, and retaliation”. The panel’s report cited “a vacuum of accountability” and “a culture of impunity”.

Byanyima’s predecessor, Michel Sidibé, was accused of protecting his deputy, Luiz Loures, who was accused of sexual assault by an employee, Martina Brostrom. Several women also alleged harassment from Loures, whose contract with UNAids has ended. Loures has denied all allegations. Sidibé, who also denied wrongdoing, initially refused to quit, stood down in May after he was appointed health minister in his native Mali.

“Definitely there is a lot of work to do to restore trust – trust of the staff in their leaders, in the organisation internally – because the scandal at UNAids was about some very senior leaders falling short of the values of the organisation,” said Byanyima in an interview with the Guardian, three weeks into the job.

“One of my immediate challenges is to see that cases that have been dragging on for a year and even longer are closed, so that staff can begin to see that we are ending impunity for abuse of power. But we also have to work on the culture of the organisation – how did that get to happen? Why did people abuse their power?”

Byanyima said she wanted to use a feminist approach to build a new culture in which everyone could work in safety and with dignity.

“The abuse of power … the sexual part is the tip of an iceberg, really. There’s so much more abuse that happens and people live – especially those at the bottom, who are mostly women – in pain. They come to work and they suffer at work. That is totally unacceptable,” she said.

“It is like being a battered woman in your household where you are often trapped. You don’t want to leave your home where there are people you love. At the same time, you are suffering. That’s what happens at work. You like the mission of the organisation, you need the salary you get, you like the colleagues you work with, but someone is making your life more painful. So we’ve got to fight it.”

When UNAids was created in 1994, said Byanyima, with an epidemic raging, power appeared to have been concentrated at the top of the organisation. She said it needed to be redistributed, with people becoming more accountable and embracing the values of the organisation, which had been damaged by the scandal.

“We have work to do. We have work to do to build trust with the external partners. We did lose credibility. I cannot deny that,” she said.

“I come with humility because I also saw the pain and the hurt and the damage to my organisation which I loved, Oxfam, because of the mishandling of – actually abuse of – power by our own staff some years ago. But when the crisis hit us, we faced it and we did not go into denial.”

Oxfam was accused last year of covering up an investigation into staff members in Haiti accused of paying women for sex after the earthquake in 2010. It emerged that the charity had allowed three men, including the organisation’s country director, Roland van Hauwermeiren, to resign without disciplinary action. It was later alleged that sex workers were also hired in Chad in 2006.

Investigations at the charity had shown that staff were largely unaware of sexual harassment but had plenty of experience of bullying. “We found a big number of our staff had witnessed someone being bullied or had been bullied themselves by somebody senior to them,” Byanyima said.

In response, she said, Oxfam’s values were put at the heart of recruitment, induction and appraisal.

“Why should you recruit a harasser because he knows how to write a policy paper on economic justice? The cost of the damage he will do, it’s not worth it,” said Byanyima, who said she did not underestimate the scale of the challenge at UNAids.

Although an estimated 24.5 million people are now able to access drug treatment to keep them healthy and suppress the virus, 1.7 million more were newly infected with HIV last year alone. Of new HIV infections among adolescents in eastern and southern Africa, four out of five cases were among girls.

“These are numbers that shame us,” said Byanyima. “They tell the story of women’s rights on our continent. They tell us that governments don’t put a priority on women and girls.

“I think UNAids is needed more today than ever before.”