Some African Union troops in Somalia sexually exploited or raped women and girls who are internal refugees, a new report by an international human rights group alleged Monday.

Human Rights Watch said it interviewed 21 women and girls since 2013 who described being sexually abused or sexually exploited by Burundian or Ugandan military personnel in two bases in Mogadishu.

Ten separate incidents of sexual abuse, including rape and sexual assault, and 14 cases of sexual exploitation were documented during the period, the rights group said. Four of the rape cases and one sexual assault involved girls under 18. The youngest victim was a 12-year-old girl who was allegedly raped by a Ugandan soldier.

Several women said the soldiers refused to wear condoms and that they had caught sexually transmitted infections as a result, according to the report. Several also described being slapped and beaten by the soldiers who forced them to have sex.

Only two out of the 21 women and girls interviewed filed a complaint with Somali or other authorities, the report said.

One 15-year-old girl went to the Burundian contingent's base to get medicine for her sick mother late 2013, the report says.

A Somali interpreter told her to follow two Burundian soldiers to get medicine. They took her to a remote area and one of the soldiers raped her, Human Rights Watch said. "First he ripped off my hijab and then he attacked me," she is quoted saying. As she was leaving, the second Burundian soldier gave her US$10, the report says.

Human Rights Watch urged troop-contributing countries, the African Union Mission in Somalia and donors to urgently address these abuses and strengthen procedures inside Somalia to seek justice.

"Some African Union soldiers have misused their positions of power to exploit Somalia's most vulnerable women and girls," said Liesl Gerntholtz, women's rights director at Human Rights Watch. "Somalia has many intractable problems, but the Somali and AU leadership could end sexual exploitation and abuse by pressing troop-sending countries to hold abusers responsible."

Human Rights Watch said all of the Somali women and girls interviewed were internal refugees from south-central Somalia.

Somalia with the help of the African Union troops is attempting to emerge from decades of conflict which has led to occasional famine.

Both the famine and conflict has displaced tens of thousands of women and girls from their communities, and from their family and clan support networks, the report says.

"Without employment options and basic resources, many must rely completely on outside assistance and are forced into exploitative and abusive situations to sustain themselves and their children," said the report.

The African Union Mission in Somalia did not have an immediate comment about the allegations. AU troops in Somalia have been previously accused of sexual abuses.

In August last year African Union mission said it was investigating allegations of rape made against its soldiers in the Somali town of Maslah. The findings of the investigations were not made public.

Since those allegations the African Union mission has held workshops to encourage officers to prevent sexual exploitation and abuse in the peacekeeping operations.