Brazil’s environment minister has resigned after becoming increasingly isolated within the government.

Marina Silva, who rose from poverty in the Amazon state of Acre to become a global figurehead for environmental activists, resigned late on Tuesday in a manner typical of her way of operating: she wrote to President Luiz Inácio Lula da Silva and immediately announced her decision to the media, leaving no room for possible negotiation.

The final straw for Ms Silva appears to have been the appointment of Roberto Mangabeira Unger, the minister for strategic affairs, to take charge of a new plan for sustainable development in the Amazon.

But during five years in the job she found herself in growing conflict with ministers pressing for the approval of infrastructure projects, many of which have been held up by the long process of obtaining environmental licences.

The most visible such project concerns the River Madeira in the Amazon, where two hydroelectric generating plants are to be built against fierce resistance from indigenous people and environmental groups. Mr Lula da Silva irritated Ms Silva by commenting that Brazil’s economic development was being held up “for the sake of a few fish”.

Many environmentalists were dismayed by Ms Silva’s departure from government, which came days after a landowner in the Amazon had a conviction for ordering the killing of a US missionary nun overturned.

Ms Silva described the ruling in the case of Dorothy Stang, apparently murdered in 2005 for her activism on behalf of landless family farmers, as “lamentable”.

In a statement, Greenpeace, the international environmental group, said Ms Silva had “taken the credibility of Lula’s government with her”. It said: “With her exit, a faction of the government which is pressing for economic development at any cost . . . has won a major victory against those who seek to reconcile development with sustainability.”

Others will be less alarmed. Ms Silva was criticised by many for seeing conservation as a “zero-sum game” and for her opposition to initiatives attempting to reconcile the interests of ranchers and farmers with conservation.

No replacement had been announced on Wednesday.