London (CNN) Sexual abuse of vulnerable women and girls by international aid workers is "endemic" and has been happening for years, with perpetrators easily moving around the sector undetected, according to a damning UK government report published Tuesday.

The inquiry heard "horrifying" stories of aid staff sexually exploiting the very people they were meant to be helping, including one homeless girl in Haiti who was given $1 by a worker for a nongovernmental organization (NGO) and raped.

The scathing report by the House of Commons International Development Committee comes after historical allegations of harassment and sexual misconduct by employees of several top NGOs, including Oxfam and Save the Children, surfaced earlier this year. Those allegations prompted the Committee to launch an inquiry into abuse in the aid sector in February.

Tuesday's report found sexual abuse and exploitation to be "endemic across the international aid sector" and targeted at both locals and staff members. Abuses ranged from unwanted sexual comments to rape.

"The power imbalance is predominantly, although not exclusively, men abusing women and girls," said the report, which warned that the cases that had come to light were likely just the "tip of the iceberg."

A cause of "deep concern and alarm" was the ease with which individuals known to be predatory or potentially dangerous were able to move undetected from one aid organization to another, the report added.

The committee also criticized aid groups for failing to tackle the problem despite being aware of reports of abuse for years. "Repeatedly, reports of sexual exploitation and abuse by aid workers and/or peacekeepers have emerged, the sector has reacted, but then the focus has faded," the report found.

Chair of the committee, MP Stephen Twigg, told CNN the report set out "the collective failure over period of at least 16 years by the aid sector to address sexual exploitation and abuse."

He said that in effect, organizations had often put "their reputation ahead of women, children and other victims of sexual exploitation and abuse."

Year of scandal for aid groups

The issue of sexual abuse in the aid sector came to the forefront in February when reports emerged that senior Oxfam staff paid for prostitutes during the 2010 Haiti earthquake relief mission.

Four staffers from the UK-based charity were dismissed and three others -- including then-country director Roland van Hauwermeiren -- resigned after an internal investigation into the allegations at the time. Oxfam was accused of covering up the findings of the investigation and criticized for failing to act on allegations of abuse sooner. The charity issued a formal apology in February to Haiti's government.

Van Hauwermeiren reportedly told a Belgian newspaper in February that reports on the allegations got some things right, but also contained "a lot of lies and exaggerations."

Days later it emerged that former Save the Children chief executive Justin Forsyth had been accused of harassing female employees between 2011 and 2015. He went on to work as deputy executive director at UNICEF in 2016 until he resigned in February

In announcing his resignation on Twitter, Forsyth wrote: "I apologized unreservedly at the time and face to face. I apologize again."

The Red Cross also announced in February that 21 staff members had been dismissed or resigned for "paying for sexual services" since 2015.

Oxfam Chair of Trustees Caroline Thomson told CNN in a statement that Tuesday's report made for "incredibly painful reading" for Oxfam and the wider aid sector.

"Oxfam exists to help improve the lives of the world's most vulnerable people; we know we failed to protect vulnerable women in Haiti, and we accept we should have reported more clearly at the time -- for that we are truly sorry," Thomson said. "We have made improvements since 2011 but recognize we have further to go. The Committee is right to challenge all of us in the sector to do better."

Similarly, Save the Children UK's CEO Kevin Watkins said in a statement that the organization had "made mistakes in our own handling of historical sexual harassment complaints from staff in the UK." He added that "although some progress has been made in creating a more respectful working culture, there is a great deal more to do. That's why we have commissioned an independent internal review of our organizational culture."

Victims suffered unwanted pregnancies, diseases

Tuesday's report noted that sexual misconduct by aid workers and peacekeepers had a "documented history stretching back nearly 20 years."

The report recounted the sexual exploitation and abuse of girls between the ages of 13 and 18 by United Nations and aid agency staff in refugee camps in Liberia, Guinea and Sierra Leone in 2001. One victim said that "an [aid] worker made me pregnant but now he left me and is loving to another young girl."

Victims suffered other problems including abortions and exposure to sexually transmitted diseases including HIV/AIDS. The devastating knock-on effects of abuse included a loss of education and skills training, reduced employment opportunities and social exclusion, the report said.

The UK inquiry was triggered by alleged abuses by Oxfam staff in the aftermath of Haiti's 2010 earthquake.

The UN refugee agency announced at the time it was launching a number of measures to combat child abuse.

Meanwhile, with the Syrian civil war in its eighth year, sexual exploitation and abuse by aid workers were "an entrenched feature" in the lives of women and girls there, particularly at aid distribution centers, the report said, citing a study by the UNFPA.

Perpetrators around the world hailed from a broad range of jobs, ranging from guards to drivers and senior managers. They were a mix of local, national and international personnel, the inquiry found.

A 'boy's club' culture

A "reactive, patchy and sluggish" response to reports of abuse, and a tendency for "whistleblowers rather than perpetrators" to end up feeling penalized, was blamed for the toxic environment.

A "boy's club" culture within organizations also meant sexual harassment and abuse of staff could thrive unchallenged, the report found. In recent months the #MeToo movement had helped shine a light on sexual misconduct, the report said, but the aid sector still had a long way to go to change.

The report called for improved processes around the reporting of sexual abuse, the safeguarding of whistle-blowing systems, and a change in culture at humanitarian organizations.

A global register of aid workers that would "act as one barrier to sexual predators seeking to enter the profession" was suggested as a way forward.

The report also said victims should be included in the policy-making process, and called for the establishment of an independent aid ombudsman to whom victims seeking justice could appeal.

One of the biggest obstacles to progress was a lack of funding, with organizations facing huge pressures to reduce overheads. The report said donors should provide funds for aid groups to implement reporting systems and safeguards against abuse.