A mysterious oil spill that has polluted shores along a vast area of Brazil’s northeast may have resulted from unspecified criminal activity, and a foreign country could be responsible, President Jair Bolsonaro said on Tuesday.

An estimated 100 tons of crude has drifted towards land since early September, polluting some of the country’s most pristine beaches and forcing Brazilian officials to grapple with yet another environmental crisis. The government has already come under close scrutiny and heavy criticism after an unusually intense season of forest fires in the Amazon.

Now, oil has been spotted on at least 132 beaches affecting 61 municipalities in nine states, the country’s Environment Ministry said.

Officials have said the state oil company, Petrobras, is not responsible for the spill and that the crude is neither produced in nor exported to Brazil.

Mr Bolsonaro told reporters on Tuesday that the government had a theory of what led to the spill, adding that a country is on “the radar”. He declined to elaborate, saying: “I can’t accuse a country. If it turns out it’s not that country, I don’t want to create problems with other countries.”

Amazon rainforest swept by fires: In pictures Show all 25 1 /25 Amazon rainforest swept by fires: In pictures Amazon rainforest swept by fires: In pictures Fire rages in the Amazon rainforest in the Brazilian state of Rondonina on August 23 Reuters Amazon rainforest swept by fires: In pictures Smoke billlows from burning tracts of the Amazon rainforest in the Brazilian state of Para on August 23 AFP/Getty Amazon rainforest swept by fires: In pictures Fire rages in the Amazon rainforest in the Brazilian state of Rondonina on August 23 EPA Amazon rainforest swept by fires: In pictures Land in the Amazon rainforest left scorched in the fires in the Brazilian state of Rondonina on August 23 AFP/Getty Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil on August 23 AFP Amazon rainforest swept by fires: In pictures Fire tears through a farm in the Brazilian state of Mato Grosso AP Amazon rainforest swept by fires: In pictures An area of the Amazon rainforest left scorched in the fires in the Brazilian state of Amazonas on August 24 AFP/Getty Amazon rainforest swept by fires: In pictures Satellite images show a series of fires in the southwest Brazilian state of Rondonia on August 15 AP Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil Reuters Amazon rainforest swept by fires: In pictures A satellite image released by NASA shows the active fires that have been detected in the Amazon region EPA Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Amazonas, Brazil Reuters Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil Reuters Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil Reuters Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Amazonas, Brazil Reuters Amazon rainforest swept by fires: In pictures Indigenous people from the Mura tribe wallk in a deforested area inside the Amazon rainforest in the Brazilian state of Amazonas on August 20 Reuters Amazon rainforest swept by fires: In pictures Fire tears through a farm in the Brazilian state of Mato Grosso AP Amazon rainforest swept by fires: In pictures Smoke billows from a stretch of fire in the Amazon rainforest in the Brazilian state of Rondonia on 23 August AFP/Getty Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Amazonas, Brazil Reuters Amazon rainforest swept by fires: In pictures Indigenous people from the Mura tribe wallk in a deforested area inside the Amazon rainforest in the Brazilian state of Amazonas on August 20 Reuters Amazon rainforest swept by fires: In pictures Smoke billows from a stretch of fire in the Amazon rainforest in the Brazilian state of Rondonia on 23 August AFP/Getty Amazon rainforest swept by fires: In pictures A view of logs felled illegally in the Amazon rainforest are seen in sawmills in the Brazilian state of Amazonas on August 22 Reuters Amazon rainforest swept by fires: In pictures A scorched patch of land in the state of Mato Grosso in Brazil on 20 August EPA Amazon rainforest swept by fires: In pictures Several fires are seen burning in the Amazon rainforest in this satellite image taken by NASA on 11 August AFP/Getty Amazon rainforest swept by fires: In pictures Smoke billows from a stretch of fire in the Amazon rainforest in the Brazilian state of Rondonia on 23 August AFP/Getty Amazon rainforest swept by fires: In pictures The sunsets behind clouds and smoke from fires in the Amazon rainforest in the Brazilian state of Rondonia on 18 August EPA

Ricardo Salles, the minister of the environment, flew over part of the affected area on Sunday and said the government was taking “urgent measures to address pollution”.

The spill prompted the state of Sergipe to declare an emergency last week, and officials there have warned residents to stop going to certain beaches. The crude oil has also set off concern about wildlife. Biologists have treated several turtles that have washed ashore covered in crude, but some have died.

The spill comes as Mr Bolsonaro’s government has come under withering criticism from abroad for weakening environmental policies and agencies while taking steps to open up protected lands in the Amazon to industries.