The United Nations secretary-general is launching an independent investigation into allegations that U.N. peacekeepers did not respond to prevent multiple cases of abuse and sexual violence against foreigners and civilians in South Sudan's capital.

The spokesman for Ban Ki-moon said late Tuesday that the U.N. chief is alarmed by the July 11 attack on a compound popular with foreigners in Juba. The Associated Press this week reported that South Sudanese troops went on a nearly four-hour rampage through the compound in one of the worst targeted attacks on aid workers in the country's three-year civil war.

Several witnesses told the AP that soldiers shot dead a local journalist while forcing the foreigners to watch, raped several foreign women, singled out Americans, beat and robbed people and carried out mock executions.