Five armed men have burst into a small-town hospital in the Brazilian Amazon, surrounded security guards and shot dead a prominent land rights activist, in the latest deadly attack on land campaigners.

Waldomiro Costa Pereira, an activist with the Landless Workers Movement (MST) was killed on Monday when gunmen stormed the hospital in Parauapebas in north-eastern Brazil’s Pará state, campaigners said in a statement.

Brazil has become one of the world’s most dangerous countries for land rights activists, with 61 killings last year, the highest level since 2003, according to the Pastoral Land Commission (CPT), a Brazilian advocacy group.

The motive for Pereira’s murder was unclear, the MST said, but the activist had been recovering in hospital from a previous assassination attempt.

“This is yet another murder of workers in the state of Pará,” the MST said in a statement.

“Impunity has become commonplace as has the action of criminal militia groups,” the group said, adding that Pereira was a longtime activist in the “struggle for agrarian reform”.

At the time of his killing, Pereira was not active with the MST and was instead devoting his time to advising the local government on agriculture, the activist group said.

Local officials in the city of Parauapebas condemned the murder and police said they were investigating the killing, the Folha de São Paulo newspaper reported.

Conflicts over territory are common in Brazil where 1% of the population owns nearly half of the nation’s land, according to a 2016 study from the University of Windsor in Canada.