A 15-year-old indigenous boy has been murdered in Brazil on the edge of a heavily deforested indigenous reserve in the state of Maranhão, on the fringes of the Amazon.

The murder, the fourth from the Guajajara tribe in recent weeks, came as a wave of racist abuse against indigenous people swept social media in the state.

The Indigenous Missionary Council(CIMI), a non-profit group reported that Erisvan Soares Guajajara’s body was found with knife wounds on Friday in Amarante do Maranhão. The group said he had travelled to the town, on the edge of the Araribóia indigenous reserve, with his father. The G1 news site reported that a non-indigenous man called Roberto Silva, 31, was also killed with Erisvan and that both died in the early hours of Friday at a party in an area called Vila Industrial.

“Another brutal crime against the Guajajara people,” tweeted Sonia Guajajara, a leader from the same tribe and reserve who is executive coordinator of Brazilian indigenous association ABIP. “Everyone who doesn’t like us feels allowed to kill because they know impunity rules. It’s time to say ENOUGH.”

Murders of indigenous people soared 23% in 2018, according to CIMI figures, and land invasions have risen since far-right president Jair Bolsonaro took office in January. He has compared indigenous people living on reserves to “prehistoric men” and said their lands should be developed.

In a statement, the state government of Maranhão said preliminary investigations indicated “the crime was not motivated by hate, land disputes or deforestation in indigenous reserves”. Brazil’s indigenous agency Funai said it was following the case.

Erisvan lived in the Araribóia indigenous reserve, which has been decimated by loggers. A group of Guajajara forest guardians expelled loggers from the reserve but have faced threats and violent attacks. In November, the guardian Paulo Paulino Guajajara was killed by loggers in an ambush and another, Laércio Guajajara, was shot and injured.

Loggers in illegal vehicles operate openly around Amarante yet police rarely intervene. “There is a lot of racism against indigenous in Amarante,” said Gilderlan Rodrigues, CIMI’s Maranhão coordinator. The group said Erisvan’s family refuted comments by local police linking the killings to the drug trade.

Last Saturday, two Guajajara leaders – Firmino Silvino Guajajara and Raimundo Bernice Guajajara – were shot and killed in a drive-by shooting on a highway in the nearby Cana Brava indigenous reserve in the same state. Two others were injured.

The men were returning from a meeting when a group of men in a white car opened fire. A Funai official said the killing could have been related to frequent robberies on the highway which crosses the reserve but Maranhão’s human rights society blamed rising prejudice.

Since then a wave of racist abuse has swept social media in the region. “Those who fired should have killed at least 50,” said one local on a WhatsApp group. “The government should throw a bomb and exterminate these disgraceful indigenous,” said another.

“These are common people … inciting crimes against indigenous people,” said Érika Nogueira, the director of the Ascalwa indigenous association. “That is what is most worrying, it is civil society.”