Millions of refugees have fled conflicts in the region
But the UNHCR confirmed on Friday that the individuals are still working in the camps in Liberia, Sierra Leone and Guinea.
"They are in place. We cannot do much without firm proof to suspend them," said UNHCR spokesman Kris Janowski.
"For the moment the proof is simply too weak to do so."
'Confusion'
Local staff employed by 40 aid agencies were implicated in testimonies gathered from 1,500 people interviewed in November 2001.
An unspecified number of children said they had been asked for sex in return for food.
Some under-age girls said United Nations peacekeepers in the West African region were involved.
The agencies, which include UNHCR itself, have not been named publicly.
Mr Janowski said there may be some confusion about which agencies the accused aid workers are employed by.
"We have absolutely no idea whether all of these agencies or some of these agencies have been involved," he said.
He said most of the organisations were only told of the allegations on Wednesday.
Poverty blamed
The girls who said they were abused were mainly aged between 13 and 18, but there have been reports that some girls were still younger.
The report cited lack of regulation and an absence of international staff as possible contributing factors.
But it said that poverty was the principle cause, with parents feeling compelled to offer their children to aid workers for sex in order to survive.
Mr Janowski said UNHCR was already trying to safeguard against further sexual exploitation of children by employing more women in the camps, although he added so far few qualified or experienced female staff had been found.
The head of the agency, Ruud Lubbers, said on Thursday that the investigation would not be extended to other parts of the world.