One of the two ethnic Chechens suspected of being behind the Boston Marathon bombings had been under FBI surveillance for at least three years, his mother said.
Zubeidat Tsarnaeva told the English-language Russia Today television station in a phone interview, a recording of which was obtained by Reuters, that she believed her sons were innocent and had been framed.
Tamerlan Tsarnaev, 26, was killed in a shootout with police and his 19-year-old brother Dzhokhar was captured after a day-long manhunt.
"He [Tamerlan] was controlled by the FBI, like, for three to five years," she said, speaking in English and using the direct English translation of a word in Russian that means monitored.
"They knew what my son was doing, they knew what sites on the Internet he was going to," she said in what Russia Today described as a call from Makhachkala, the city where she lives in Russia's Dagestan region.
Tsarnaeva echoed the boys' father, Anzor, who said on Friday that he believed they had been framed.
"It is really, really a hard thing to hear. And being a mother, what I can say is that I am really sure, I am, like, 100 percent sure, that this is a set-up," she said.
U.S. government officials have said the brothers were not under surveillance as possible militants. But the FBI said in a statement on Friday that in 2011 it interviewed Tamerlan at the request of a foreign government, which it did not identify.
It said the matter was closed because interviews with Tamerlan and family members "did not find any terrorism activity, domestic or foreign."
The FBI statement was the first evidence that the family had come to security officials' attention after they emigrated to the United States from Dagestan about a decade ago.