Award-winning Burundian humanitarian worker Marguerite Barankitse has denied any role in recent deadly attacks in the country's economic and political capitals.
A series of grenade attacks on Gitega and Bujumbura earlier this week claimed the lives of four people and injured more than 100, security officials said.
Ms Barankitse, who has been nicknamed "the angel of Burundi" for adopting thousands of children displaced by war over the years, was accused by the state prosecutor of planning what he described as terrorist acts.
"The allegations seek to scare me and discourage my charitable activities, but I am not afraid. I am standing tall," Ms Barankitse told the BBC Great Lakes service.
She now lives as a refugee in neighbouring Rwanda.
Also named as suspects were former journalist Alexis Sinduhije and François Nyamoya. They're in exile and leading the Movement for Solidarity and Democracy opposition party.
Mr Nyamoya said the allegations were baseless and politically motivated.
Burundi has issued international arrest warrants for all three.
Early this year, Ms Barankitse and former army officers, journalists and activists in exile were sentenced in absentia to life for taking part in the 2015 failed coup that plunged Burundi into crisis.
Ms Barankitse, who is a critic of Burundi's government, said she played no part in the unsuccessful putsch.