Brazil's Petrobras has cleaned up 133 tonnes of oil along Brazil's northeastern shoreline, although the state-controlled company is adamant that it is not the source of any of the mysterious spills.

"We have analysed 23 samples collected from the affected areas and none of this oil comes from oil produced or marketed by Petrobras. This is a very strange business and shows no sign of improving yet,” Petrobras chief executive Roberto Castello Branco told a mining and energy committee in Brazil's Chamber of Deputies.

Spills have been detected on about 100 beaches in the states of Alagoas, Pernambuco, Paraiba, Rio Grande do Norte and Ceara over the last week. These are all regions where tourism is a major money earner and marine life - such as turtles - has been adversely affected.

Castello Branco's words echoed those of President Jair Bolsonaro, who told reporters that molecular tests had found that the crude found on the beaches was not from Brazilian oilfields and he suggested that the oil could have been dumped "criminally".

While no official word has been given about the origin of the mysterious oil spill, Brazilian news magazine Epoca reported that Petrobras sees Venezuela's PDVSA is the main suspect, although no evidence was cited.

Castello Branco used his congressional visit to state that Petrobras must keep investing at least $3 billion per year in exploration in order to incorporate new reserves at a targeted rate of 1 billion barrels per year.