Russian authorities secretly wiretapped the mother of the Boston bombing suspects and recorded her discussing jihad in vague terms during a 2011 telephone conversation, CNN reported on Saturday.
The Russians only turned over the information to their U.S. counterparts in recent days, according to the report.
A U.S. official with knowledge of the investigation who confirmed the intercept to the network declined to confirm who was on the other line.
Asked about the report as he attended the White House Correspondents' Dinner, Attorney General Eric Holder declined to comment, saying it was an "ongoing matter."
The conversation raises the possibility that red flags were missed that could have alerted U.S. officials to the threat posed by the Tsarnaev brothers, accused of killing three people and wounding 264 during twin blasts at the Boston Marathon this month.
Both the CIA and the FBI flagged deceased Boston bombing suspect Tamerlan Tsarnaev over possible terror ties after Russian officials contacted the U.S. agencies in 2011.
Reports said Russian authorities had also alerted their U.S. counterparts about concerns that his mother, Zubeidat Tsarnaeva, was a religious extremist, and that she was added along with her older son to a terror watch list.
At the time, the FBI said Russia did not respond to U.S. requests for additional information, and U.S. investigators saw no reason to pursue the investigation further.
The report comes several days after the mother launched an impassioned attack on the U.S. authorities, blaming them for her son’s death.
Tamerlan was "killed, cruelly killed. I want to scream to the whole world, what did you do? He was alive!" Zubeidat, dressed in an Islamic headscarf, said on Thursday.
"He was alive! Why did they need to kill him? Why? They got him alive," she added, reaffirming her belief that her sons were innocent of the Boston bombings. "I know one thing, that my children did not do this."
The surviving bombing suspect, Tsarnaev's 19-year-old brother Dzhokhar, is being held at a federal prison medical center where he was transferred early Friday, after spending several days in the same hospital as some of his alleged victims in Boston.
Dzhokhar Tsarnaev has been charged with using a weapon of mass destruction and could face the death penalty if convicted in U.S. federal court.
On Wednesday, the interfaith group Americans for Peace and Tolerance said that the mosque attended by the two brothers “has a curriculum that radicalizes people.”
The mosque has reportedly been associated with other suspected terrorists and is affiliated with the controversial Muslim American Society, APT said.