Two Landless Workers Movement (MST) activists, brothers Edilson Rufino da Rocha, 37, and Francisco Manuel de Lima 27, were shot in their beds by armed assailants on Friday near the town of Passira, 66 miles west of Pernambuco state capital Recife.
A third, Josuel Fernandes da Silva, 33, was gunned down by three assassins on Thursday in Sao Jose da Coroa Grande, around 68 miles south of Recife, an MST leader said.
"They were victims of landowner gunmen in reprisal attacks," MST leader Edilson Barbosa said by cellphone from a funeral for two of the dead activists.
The latest killings came weeks after five landless activists were shot by assailants in the central Brazilian state of Minas Gerais.
They came amid a rising number of MST land occupations meant to speed President Luiz Inacio Lula da Silva's slow-moving land reform.
Brazil's human-rights secretary Nilmario Miranda was set to attend the funeral of the two activists and investigate the killings, which follow MST attempts to occupy a local ranch, state news agency Radiobras reported.
Under Brazil's constitution, farmland that is not used can be expropriated by the government and redistributed to some of
the hundreds of thousands of peasants waiting for plots in encampments across Brazil.
The MST grabs land to force legal decisions on possible expropriation. The invasions prompt clashes with landowners who form militias to protect property.