"Many children are showing evidence of neurological damage. Environmental investigations have found very high concentrations of lead both outside and inside people's homes," the WHO said in a statement.

Some 950 people in the poor area are "continuously exposed through ingestion and inhalation of lead-contaminated dust," it said. "Thorough decontamination of the affected area of NGagne Diaw, including the insides of homes, is a high priority."

At least 31 children require treatment for lead poisoning, but only a proportion of the population has been examined, said Joanna Tempowski, a scientist in the WHO's environmental health emergencies division.

"The focus is on small children because they are very vulnerable to lead poisoning because neurotoxic substances can affect child development even at quite low levels, and these are very high levels," she told Reuters.

Senegal needs urgent technical and financial assistance from the international community for the clean-up, the WHO said.

"The recycling has stopped but the lead is in the environment and won't disperse. It needs to be removed. It is an enormous job," said Tempowski, who stressed that some of the batteries may also contain other contaminants such as arsenic.

Senegal's health ministry reported to the WHO in March that a total of 18 children died between last October and February, WHO spokeswoman Sari Setiogi said.

Many community members in NGagne Diaw were directly engaged in battery recycling as a source of income.

Siblings and mothers of the dead children had "extremely high blood level concentrations" -- in many cases more than 10 times the level which may impair neurological development, according to the Geneva-based United Nations agency.

Adults and children not directly involved in lead recycling also showed dangerously high levels.

Senegalese children with high lead exposure may need chelation therapy, which removes heavy metals from the body, the statement said. But the WHO warned the treatment would be "ineffective and may exacerbate toxicity" in children who are still exposed to lead.

The agency has provided chelating agents and its clinical toxicologist has started training local medical staff, it said. (Editing by Laura MacInnis and Giles Elgood)