One nephew, Tamerlan Tsarnaeva, 26, was killed after exchanging gunfire with police in the Boston area and the other, Dzhokhar Tsarnaev, 19, was arrested Friday following a subsequent manhunt.
Maret Tsarnaeva told the Canadian Broadcasting Corp. in a telephone interview the FBI were relying on photos of her nephews walking on a street near the marathon finish line Monday when two bombs went off, killing three people and injuring scores more.
"My nephews cannot be part of this terrible, horrible act that was committed in the streets of Boston," she said.
"I know these two nephews -- smart boys, good boys -- they have no motive for that. They have no ideas to be going to this kind of act. It's just not the case, it cannot be true."
She said the fact the pair were carrying backpacks near where the bombs went off was not cause for suspicion.
"It's Monday, they are walking, maybe, you know, walking around for their business. Backpacks? How can this be suspicious, carrying backpacks? At the age of these boys," she said.
She contends her nephews were targeted by authorities because of their Chechen background, the CBC said.
She said she hadn't seen the pair in five or six years but had spoken with Tamerlan a year ago. She said he was married and had a daughter.
Tsarnaeva said Tamerlan was staying at home taking care of his daughter while his wife worked. She said he became more interested in his Muslim faith about two years ago, and started praying five times a day.
She said Tamerlan visited the brothers' father, Anzor, in Makhachkala, the capital of the Russian republic of Dagestan, which borders Chechnya, a year ago.
She said Anzor was once beaten in the streets of Boston and their own father was "blown to pieces" in an unexplained incident in a car in Kyrgyzstan years ago.
Tsarnaeva said the family came from Kyrgyzstan, but their ethnicity is Chechen. She said Chechens have been subjected to persecution for generations, and she and three of her siblings became lawyers to better protect themselves.
"All together, we've been tossed around," she said. "Deported from here as Nazi collaborators, then there, then here. Enough."