An investigation by the government in Liberia has concluded that the Firestone Rubber Plantation Company has polluted local water sources.

The three-month investigation found that a plant south-east of the capital Monrovia was responsible for high levels of orthophosphate in creeks.

The report called on Firestone to improve its waste treatment facility.

Firestone said it believed it fully complied with environmental law and its waste water was not harmful to health.

Sample testing

The Firestone plant is about 48km (30 miles) south-east of Monrovia and the creeks are a water source for tens of thousands of villagers.

Many residents had said they could no longer use the water.

The BBC's Jonathan Paye-Layleh in Monrovia says residents in the town of Kpanyah town had been complaining of developing skin rashes on venturing into affected creeks.

The investigation team included government ministries, Firestone representatives and local residents.

Water samples were collected and tested at the American University of Beirut in Lebanon. Testing was also carried out in Liberia.

The tests confirmed high levels of orthophosphate.

The report called on the management of Firestone to adhere to the Environmental Protection and Management Law.

Firestone said it believed it was in full compliance with the law and with its environmental commitments to the government and that it "strongly disagreed with any characterisation to the contrary".

It said an external consultant had found the plant's waste water was not harmful.

Firestone said that phosphate was also not harmful to human health but that it would work to address any elevated levels.

It said it believed its water treatment system was working as designed and intended.