At least 131 people to receive some form of protection after series of assassinations in tussle over land and resources

The Brazilian authorities are to provide government protection to activists threatened with murder following a series of killings in the Amazon.

The measures, announced on Tuesday, should see at least 131 people receive some form of protection, among them environmental activists, rural leaders and human rights defenders.

"The most important thing is to guarantee that those behind the threats are identified, held responsible and punished," said Brazil's human rights minister, Maria do Rosário, launching the measures. "Among those who are threatening people today are some who have killed in the past and enjoyed impunity."

An official from Brazil's human rights secretariat said the protection would come in "various different modalities", ranging from regular visits to 24-hour armed security. Protection would be given to those cases considered "serious" but would not necessarily involve "individual treatment"," the official said.

Several human rights activists in the Amazon already have permanent armed security.

Murders are nothing new to the Brazilian Amazon, where an ongoing tussle for land and natural resources continues to claim lives. But the violence made international headlines in May when two rainforest activists were ambushed and killed near their home in Nova Ipixuna, Pará state.

José Cláudio Ribeiro da Silva and his wife, Maria do Espírito Santo, had spent more than a decade fighting illegal loggers, ranchers and charcoal producers, and had repeatedly alerted local and federal authorities to the threats they suffered as a result.

"I could be here today talking to you and in one month you will get the news that I disappeared," Ribeiro told a TEDx conference in Brazil in November. "I will protect the forest at all costs. That is why I could get a bullet in my head at any moment … because I denounce the loggers and charcoal producers, and that is why they think I cannot exist."

A month after the couple's deaths, no arrests have been made, but few doubt it was the work of hired guns, known as pistoleiros. Part of one of Ribeiro's ears was cut off by his killers – apparently a means of proving the assassination had been carried out. In an interview at the end of last year, Ribeiro told one Brazilian TV channel he had a R$5,000 (£2,000) price on his head.

Calls for government action grew last month after another four killings in the Amazon. Members of a special paramilitary national force were deployed to the region and Brazil's environmental agency, Ibama, launched a series of operations against illegal loggers and charcoal producers. Last week a team of Ibama operatives shut down 12 illegal sawmills in Nova Ipixuna, with support from heavily armed members of the army and federal police.

Following the murders of Ribeiro and his wife, activists handed the federal government a list of 207 people who had received death threats, of whom 42 had already been killed. "We cannot offer police escorts to all of the threatened names," Rosário said at the time. "It would be unrealistic to say we were in a position to attend a list with so many names."

One of the highest-profile Amazon killings in recent history was the murder of Dorothy Stang. The the 73-year-old American nun, a well-known social and environmental activist, was gunned down near the town of Anapu in February 2005. She reportedly read an extract from the Bible to her killers moments before being killed. "Blessed are the poor in spirit, for theirs is the kingdom of heaven," she told them.

Her brother, David Stang, said she had been defiant to the end. "She called me the day before her murder and said, 'I will not run away from these people,'" he told the Guardian during a 2009 trip to Brazil.

"The needs of the people are not being met," he added. "They are being murdered. They are being impoverished. The land is being destroyed."

In the wake of Stang's murder the Brazilian government dispatched hundreds of federal troops to the region to restore order. But six years on those forces have now withdrawn from Anapu and local activists claim the violence has returned.

Even the police chief, Melquesedeque da Silva Ribeiro, this week admitted fearing for his life, after conducting a recent operation against illegal deforestation. "I fear threats from diverse sectors," he told Brazilian reporters.

According to the CPT, a Brazilian human rights group that compiles annual lists of the country's "walking dead", 918 people were killed in the Brazilian Amazon between 1985 and April this year. Trials were held in just 27 of the cases, the CPT claimed.