UNITED NATIONS - Four UN peacekeepers in southern Sudan have been sent home in the past year following investigations of alleged sexual abuse and the United Nations is looking into reports that more than 20 children were raped and abused, the UN spokeswoman said Wednesday.

Michele Montas said the United Nations was "deeply concerned" by a report in a British newspaper alleging that UN personnel in Juba, the capital of southern Sudan, were involved in sexual exploitation and abuse. The UN was trying to determine whether the allegations were new or involved existing cases already under investigation.

The Daily Telegraph, citing an internal report by the UN children's agency along with interviews with more than 20 victims of the purported abuse, reported that the alleged abuse began two years ago when the UN Mission in Southern Sudan, known as UNMIS, arrived to help maintain peace in the region after a more than two-decade civil war.

"The first indications of sexual exploitation emerged within months of the UN force's arrival and The Daily Telegraph has seen a draft of an internal report compiled by the UN children's agency UNICEF in July 2005 detailing the problem," the paper reported on its Web site. "Evidence suggests that UNMIS staff may already be involved in sexual exploitation."

A 14-year-old boy told the newspaper: "I was sitting by the river the first time it happened." A 13-year-old boy told the paper he was lured to a UN car with the offer of cash, abused and dumped by the side of a road.

Montas told reporters the UNICEF report "did not talk about sexual abuses from UN peacekeepers."

"They spoke about sexual abuses on the part of the Sudanese military," she said.

Nonetheless, Montas said, "the UN is very concerned about this issue and over and over again repeated its determination to end sexual abuse by peacekeepers."

"The UN standard on this issue is clear ¡ª- zero tolerance, meaning zero complacency and zero impunity," she said.

The Office of Internal Oversight Services, the UN's internal watchdog known as OIOS, has a team permanently based in Sudan, where more than 11,000 peacekeepers, police and international civilian staff are based and it investigates all allegations of abuse. OIOS also has teams in Congo, Liberia and Haiti, where the UN has other large peacekeeping operations.

"Over the past year, as a result of UN investigations, four UNMIS peacekeepers have already been repatriated," Montas said. The nationalities of the peacekeepers was not released.

While allegations of abuse have dogged peacekeeping missions since their inception more than 50 years ago, the issue was thrust into the spotlight after the United Nations found in early 2005 that peacekeepers in Congo had sex with Congolese women and girls, usually in exchange for food or small sums of money.

The UN peacekeeping department instituted a new code of conduct for peacekeepers, new training for officers and all UN personnel, and reinforced messages against sexual abuse.