The talks, which will not include the details of Morales' proposed new constitution, are set to begin on Thursday.
Cossio agreed to the talks despite the arrest of Leopoldo Fernandez, the governor of Pando province and one of the rebel state leaders, who is accused of involvement in the deaths of pro-Morales farmers during protests last week.
The attorney-general said Fernandez, a member of the Podemos opposition party, would be investigated over accusations of genocide.
Morales and Hugo Chavez, the Venezuelan president, both expelled the US ambassadors to their countries last week, saying Washington was supporting the opposition against Morales in Bolivia.
The US responded by expelling the Bolivian and Venezuelan envoys to Washington.
During the protests anti-Morales groups ransacked and occupied dozens of government buildings, blocked roads and sabotaged natural gas pipelines, temporarily cutting off exports to neighbouring Argentina and Brazil.
Morales, a former coca-leaf farmer and the country's first indigenous leader, has often accused the opposition in the eastern provinces of being motivated by racism.
He says his proposed new constitution would reverse centuries of discrimination against Bolivia's indigenous majority, but his opponents fear he will tighten state control of the economy and break up wealthy land owners' ranches.