Deforestation in the Brazilian Amazon is on the rise sharply, sparking alarm over the future of the world's biggest rainforest.

Between June and last August, Imazon, the first independent monitoring system for the area, detected a 100 percent surge in the clearing of land.

That's in stark contrast to last year, when deforestation fell to 4,751 square kilometers (1,834 square miles), its lowest level in decades.

The government insists a full picture will only emerge at the end of the year, once more reliable satellite images are factored in.

Provisional government data until May had pointed to a 30 percent increase.

The surge in deforestation coincides with major infrastructure projects and a new forestry law.

The law, which curbs the use of land for farming and mandates that up to 80 percent of privately-owned acreage in the Amazon remain intact, took effect last October.

It was passed by Congress where a pro-agribusiness bloc holds considerable sway.

"One of the reasons for the rising deforestation was the forestry code," said Justiniano Nett, of the Green Towns conservation group in the northern state of Para.

"It led to rumors that producers interpreted as an amnesty."

Paulo Adario, a Greenpeace official in charge of monitoring the Amazon, said the government continued to launch major infrastructure projects without creating new protected areas or demarcating indigenous lands that serve as barriers to deforestation.

"At the same time, it needs support from a political front that includes an increasingly powerful agribusiness sector and a very clear agenda of reviewing policies affecting indigenous people and protected areas," he added.

Amazon natives are up in arms over initiatives under discussion in Congress that would allow mining companies or ranchers to operate on their lands.

They are also protesting a bill that would make Congress the authority on territorial claims, which they fear would give political advantage to white ranchers.

Ranchers often clash with indigenous groups over land rights.

Under the current system, a government agency conducts studies and makes decisions about land demarcation.

"It is a process of violent assault on indigenous rights," said Cleber Buzzatto, executive secretary of the Indigenous Missionary Council CIMI.

In April, leaders of 121 indigenous tribes stormed the House of Deputies in Brasilia and protested outside President Dilma Rousseff's office to demand the return of their ancestral lands.

Indigenous peoples represent less than one percent of Brazil's 194 million citizens and occupy 12 percent of the country's territory, mainly in the Amazon.

Experts were reluctant to conclude that the latest deforestation figures signal a new upward trend in a country that managed to cut the process by more than 80 percent in eight years.

But they warned against complacency.

"Brazil is well equipped to continue bringing deforestation down, but it cannot loosen the rules," said Adalberto Verissimo, an Imazon researcher.

"It must make clear that it will not accept amnesties and will be tough against those who deforest."

Other analysts highlight a new trend: land speculation fueled by major infrastructure projects such as hydro-electric dams, highways or ports that offer prospects of economic development.

"Brazil needs to invest in prevention," said Ian Thompson, head of the Amazon project at The Nature Conservancy.