RIO DE JANEIRO: Police are investigating the cause of a fire in the new Arena Pantanal in Cuiaba which is scheduled for use during next year’s World Cup finals.

Stadium officials reported that three fire engines and other services were summoned after polystyrene insulation panels stored in the basement caught light.

No significant damage was caused to the structure of the stadium which is expected to be completed by the end of December, the deadline set by world federation FIFA.  The stadium, in the north-west of Brazil, is due to host four matches at Brazil 2014.

A police department spokesman said specialist investigators were examining the cause of the fire out of concern that it was set deliberately by protesters angry at the revenues being spent on World Cup preparations.

Sporadic riots have continued across Brazil ever since the end of the Confederations Cup in June when millions of Brazilians took to the streets to protest at  a perceived imbalance between the costs of the World Cup and social welfare spending.

More than 60 people were detained in Sao Paulo on Friday after a demonstration at a bus depot which left the building and one vehicle badly damaged by fire.

The initial demonstrations, in Sao Paulo in early June, were sparked by anger over bus fare price rises.