The United Nations is investigating some 150 allegations of sexual abuse by UN civilian staff and soldiers in the Democratic Republic of Congo.
Some 10,000 UN troops serve in DR Congo
Accusations include paedophilia, rape and prostitution at a UN site in Bunia, says UN official Jane Holl Lute.
She told a news conference that there was photographic and video evidence for some of the allegations.
Reports of abuse involving Monuc troops first surfaced last year, prompting the UN's internal watchdog to launch an inquiry.
"It's important that those missions be above reproach," the assistant secretary-general for peacekeeping operations said.
"We are shining a light on this problem in order to determine its scope, and we will not stop there."
After being briefed on its progress, Mr Annan expressed his outrage on Friday saying that a small number of civilian and military personnel had committed "shameful" acts of gross misconduct.
He said that those involved must be held accountable.
The UN mission in DR Congo now consists of about 10,000 troops and was first deployed in 2001, two years before a major war there ended.
Extreme sexual violence has been an integral part of conflicts throughout eastern DR Congo and many girls are reluctant to testify against those in authority.
A UN probe rejected similar allegations of sexual exploitation of refugees by UN staff in West Africa two years ago.