Among the accusations being investigated is that pimps are using the presence of UN peacekeepers to lure girls to work as prostitutes in South Kivu, the mission said in a statement on Thursday.

The UN's 17,000-strong mission, known as Monuc, which is backing a string of peace deals in the vast African nation following a 1998-2003 war and helping to run elections, last year banned sex with locals.

Monuc's statement said: "Although the majority of their patrons are Congolese soldiers and civilians, some of the girls involved mentioned that elements of Monuc contingents based in the region were also among their clients.

"Monuc takes these allegations very seriously and has expressed extreme shock at the testimonies of the victims."

The UN mission said it had launched an investigation into the allegations and stressed that there would be zero tolerance of sexual abuses.

Culture of dismissiveness

Last year, the UN barred peacekeepers in Congo from fraternising with locals after investigations found some soldiers and civilian staff were guilty of rape and paedophilia including enticing hungry children with food or money for sex.

But earlier this year, a UN diplomat responsible for monitoring how the world body was tackling the problem said sexual abuse charges remained unacceptably high due to a persistent "culture of dismissiveness" in field missions.

Hungry children are particularly
vulnerable to sexual exploitation

The UN said on Thursday: "Monuc will work in close collaboration with its local partners to fully investigate the matter, contribute to the eradication of this prostitution ring and to the arrest of its backers by the Congolese authorities."

Despite the presence of the world's largest peacekeeping mission, violence continues in Congo's east where local and foreign rebel groups still roam three years after the war officially ended. Government army units are in disarray.

The last Congo war sparked a humanitarian disaster that has killed about four million people since 1998, more than any other crisis since the second world war.

Civilians have frequently been targeted in fighting and sexual violence is widespread and seldom punished. The UN said it would ensure victims of the "trafficking" were protected.