Analysis showed the oil found was of a type not produced in Brazil, the environmental agency Ibama said.

There is no evidence that fish and shellfish have been contaminated but at least six sea turtles and a seabird have been found dead.

A clean-up operation is under way in the areas affected.

The spill, first detected on 2 September, spans over 1,500km (932 miles) and has been detected in 105 locations in eight states, affecting wildlife and popular beaches including Praia do Futuro in Ceará, and Maragogi, in Alagoas.

Molecular analysis of the oil by Brazil's state-run company Petrobras showed the crude oil spilled did not originate in the country, Ibama said in a statement (in Portuguese).

The test also determined the oil came from a single source which has not yet been identified.

Two oil barrels have been found on the coast of Sergipe state

Crude oil is tested before being exported to make sure it follows the standards of the refinery it is being sent to, and can be identified by its chemical elements, Reuters news agency reports.

Authorities believe the spill could have been caused by a tanker transporting oil far from the coast. Two oil barrels have been found on two beaches off Sergipe state, local authorities said.

Beachgoers and fishermen have been urged to avoid the material.

Two sea turtles rescued alive were returned to the sea by beachgoers while another was sent to a rehabilitation centre.

The situation was said to be stable in the most-affected state, Rio Grande do Norte, while efforts were now being focused on Maranhão - part of the Amazon rainforest region - where new spills were being reported.

"We've never had an accident like this in Brazil... It's the first time we're seeing an accident with an undetermined source affecting so many states," Ibama co-ordinator Fernanda Pirillo was quoted by Agência Brasil news agency as saying.

Petrobras said it would deploy some 100 employees in the clean-up effort despite not being involved in the spill.

States affected by oil spill

1 - Sergipe; 2 - Alagoas; 3 - Pernambuco; 4 - Paraíba; 5 - Rio Grande do Norte; 6 - Ceará; 7 - Piauí; 8 - Maranhão

Anna Carolina Lobo, a co-ordinator of the marine programme at WWF conservation group in Brazil, said the case exposed how fragile the country's surveillance system was.

"Brazil has few boats and analysts to follow what happens in our waters," Ms Lobo was quoted by Associated Press as saying.

She said state support for such surveillance was receding even further under the government of far-right President Jair Bolsonaro.

The president, who came to office in January, has repeatedly criticised the work of non-governmental groups and activists, and slashed the budget of environmental agencies, including Ibama.