(CNN) -- African Union soldiers stationed in Somalia have raped and sexually exploited women and girls on their military bases, Human Rights Watch says in a new report.
The report released Monday accuses soldiers of working through Somali go-betweens to use a variety of ploys, such as humanitarian aid, to force women and girls to have sex as well as to sexually assault women who came to the bases seeking medical help or water.
"Some African Union soldiers have misused their positions of power to exploit Somalia's most vulnerable women and girls," said Liesl Gerntholtz, executive director of the women's rights division at Human Rights Watch.
The rights group said it interviewed 21 women and girls who recounted being raped or sexually exploited by Ugandan or Burundian troops serving with the African Union Mission in Somalia since 2013.
Among the cases described in the report is a 15-year-old girl who was allegedly raped by a Burundian soldier after she went to a military base to try to get medicine for her sick mother.
African Union challenges report
The African Union said it was "concerned" by the report and would "thoroughly" investigate the allegations. But it took issue with much of the content of the document, accusing it of "imbalance, inaccuracies and partial view."
The regional body said the portrayal of the AU mission and the broad conclusions in the report "constitute a misrepresentation of the sacrifices, achievements and genuine commitment" of the mission.
AU troops are in Somalia to support Somali forces cracking down on Al-Shabaab, a group fighting the government in hopes of turning the country into a fundamentalist Islamic state.
The mission's mandate includes helping with humanitarian assistance in Somalia, which is plagued by war, poverty and famine.
Scale of problem unclear
The AU said the Human Rights Watch report "uses a small number of cases to arrive at a generalized conclusion."
The rights group said it didn't "assess the scale or prevalence of the abuse" because of the sensitivity of the subject and the "profound reluctance" of victims and witnesses to speak out.
"Nonetheless, the findings raise serious concerns about abuses by AMISOM soldiers against Somali women and girls that suggest a much larger problem," the report said.
It called on the countries who contribute troops, the AU and donors to the mission to "urgently address these abuses and strengthen procedures inside Somalia to seek justice."
The AU said in its statement it had developed mechanisms "to prevent and respond to issues of misconduct and abuse in peace support operations, in accordance with the AU's zero-tolerance policy on this matter."
Contacted for comment, a spokesman for the mission referred CNN to the AU statement.
Somali government to launch investigation
The Somali Prime Minister's office issued a statement Tuesday expressing concern over the "grave allegations" in the Human Rights Watch report.
"The government condemns all forms of abuse against the Somali people and remains committed to ensuring perpetrators of any crime against its civilians are brought to justice," the office said.
"The government will lead a rigorous and prompt investigation into the allegations with all stakeholders and necessary action will be taken as required."