Brazil's environment minister questioned on Friday the effectiveness of the Amazon Fund created to contain the deforestation of the vast rainforest, the latest challenge to environmentalists from climate-change sceptics within the far-right government of President Jair Bolsonaro.

In a press conference at the Brazilian Institute of Environment and Natural Resources, Ricardo Salles cited numerous alleged irregularities in contracts between non-governmental organizations and the fund, challenging a belief among scientists and climate change experts that the fund efficiently contributes to anti-deforestation efforts.

Salles, who has said in the past that agribusiness in Brazil was "under threat," said there was a need to create "indicators that could tangibly demonstrate the concrete result of the use of resources."

The fund was created in 2008 to receive donations to help prevent, monitor and combat deforestation in the nearly 7 million square kilometer area, which is extremely rich in biodiversity.

Norway is the fund's main contributor, having given $1.2 billion between 2008 and 2018, official data shows. The other two major donors are Germany and Brazilian oil company Petrobras.

The environmental agenda of Bolsonaro, who questions the reality of climate change and has pledged to further open the Amazon to development, has been harshly criticized by activists and the opposition.

Before coming to power, the former army captain said environmental groups in Brazil hindered economic development and vowed that if elected, "not a centimeter" more of land would be demarcated for indigenous reserves.

He also threatened to follow the footsteps of U.S. President Donald Trump and withdraw Brazil from the Paris climate agreement. He later backpedaled on the promise, but activists and experts say the administration's agenda would make it impossible for Brazil to meet the accord's objectives.

Environmental specialists consulted by The Associated Press said they believed the fund helped anti-deforestation efforts, but emphasized it was a tool that could not solve the problem alone.

"Salles says it does not work but he has never gone to the field to analyze the Amazon," argued Adriana Ramos, director of the Socio-Environmental Institute and former member of the Fund's advisory committee.

On Friday, Salles presented to the press the summary of a ministry audit into contracts signed by the Amazon Fund in recent years. He said the ministry evaluated, over a period of 90 days, a quarter of the 103 current contracts and that they found irregularities in all of them. However, he did not give any specific cases, citing confidentiality clauses until a review by auditors.

In his presentation, the minister highlighted that 82% of the contracts were awarded without having gone through a tender. He said the ministry will push for new rules to increase supervision over the fund's activities.

Marcio Astrini, public policy coordinator for Greenpeace Brazil, said Salles sought to "destroy the entire agenda of environmental protection" in Brazil.

Last year deforestation recorded its worst rate in a decade, with a 14% increase between August 2017 and July 2018, which analyst are attributing to uncontrolled logging and land invasion.