Oxfam has dismissed 22 members of staff over allegations of sexual abuse in the last year, according to figures released by the aid charity.

Two staff members resigned before investigations were complete, with concern rising about the organisation’s management of its overseas network.

Oxfam has faced criticism following a renewed focus on sexual exploitation in the aftermath of the scandal surrounding the Hollywood movie mogul Harvey Weinstein.

Last week, Lesley Agams, Oxfam’s former country director in Nigeria, told the Times she had been assaulted by a colleague in 2010. Agams said that a few months after reporting the attack, which took place after a visit to the charity’s headquarters, her contract was terminated.

Oxfam said it dealt with 87 claims of sexual exploitation and abuse involving its workers in the year ending April 2017, which was a 36% increase on the previous year.

Oxfam told the Thomson Reuters Foundation it had referred 53 of the complaints to police and other services, while 33 were internally investigated, with about three-quarters resulting in disciplinary action.

Oxfam has 5,000 staff and thousands of volunteers in the UK and overseas.

A spokesman for Oxfam said the charity was “not unique”.

“We continue to learn and seek to improve not just in how we handle complaints but also in changing the culture in which we work to prevent the abuse of power in the first place and support those that speak out,” said a spokesman for Oxfam.

“Oxfam is not unique. Sexual abuse is a serious problem in society. We all, including Oxfam, need to get better at preventing and dealing with sexual abuse but as an international organisation fighting for women’s rights we have a special responsibility to practise what we preach and protect our staff, volunteers and beneficiaries from sexual harassment and abuse.”

Megan Nobert, a campaigner who set up the Report the Abuse NGO, which gathered information about sexual abuse in the humanitarian sector, said she was not surprised by the Oxfam allegations.

She said: “I have seen this sort of behaviour in any number of NGOs and other organisations.

“If anything, it’s good that Oxfam is admitting to these figures, because at least they are not sweeping them under the carpet. There is a serious problem with abuse across the humanitarian community.”

Nobert, who set up Report the Abuse after being attacked herself, said that charities had improved their management of allegations.

“There has been a lot of silence and stigma, but it is being reported more now,” she said. “There was a lot of retaliation over whistleblowing, even though it is 2017.”

Nobert said that, in several examples, alleged attackers had been transferred to different countries, rather than facing discipline procedures from their employers. She also said that abuse of local people was a serious problem.

In a survey of more than 1,000 individuals, Report the Abuse found that 87% of people working in the humanitarian field knew a colleague who had experienced sexual violence in the course of their work.

It found that 41% of aid workers had seen an incident of sexual violence against a colleague, while 72% of the individuals who responded to the survey said they were survivors of sexual violence.

The Charity Commission said it had contacted the trustees of Oxfam over the abuse claims.

A spokesman for the charities’ watchdog said: “We are in contact with the charity to establish both how the trustees are responding to the individual allegations, as well as to reassure ourselves that they are taking steps to ensure the charity is appropriately safeguarding all people who come into contact with it, including its staff and volunteers.”

A spokesperson for the Department for International Development said the government required a “zero tolerance” policy on sexual misconduct.

“We expect our partners to have robust systems and processes in place to prevent such behaviour,” the spokesperson said.

“Oxfam have informed us that they are investigating these allegations and we expect this to be carried out as a matter of urgency and in full compliance with the Charity Commission.”