Russian intelligence refused to pass key details about the Boston bombing suspects to the FBI, even after they had flagged them as a potential security threat.
That is according to a new report from the FBI, which claims the Bureau requested additional information on the suspects two years before the bombing.
The report, cited in the New York Times, goes on to allege that the Russians supplied critical information, such as the conversation between Tamerlan Tsarnaev and his mother on Islamic jihad, only after the bombing took place.
In 2011, Russian intelligence alerted the FBI about Tamerlan, who they said "was a follower of radical Islam and a strong believer".
The Russians also warned their American counterparts that they observed changes in the would-be bomber as he planned, and made, a trip to Russia where he supposedly met radical groups linked to Chechen rebels.
The report claims that, in response, the FBI made an initial analysis of Tamerlan and approached Russia for further information on him. However the agency did not receive the information until it was too late.
"They found that the Russians did not provide all the information that they had on him back then, and based on everything that was available the FBI did all that it could," a senior official briefed on the latest report told the NYT.
Tamerlan Tsarnaev and his brother Dzhokhar, Chechen Muslims, are believed to have set off two pressure cooker bombs at the Boston marathon finish line on 15 April last year. Three people were killed and about 260 wounded in the attack.
While 26-year-old Tamerlan died in an encounter with police days after the bombing, his brother Dzhokhar is facing trial in the US. The prosecution has sought the death penalty for the suspected bomber.
The new revelation has come barely a week before the first anniversary of the bombing.
It was reported in March that the FBI had missed an opportunity to apprehend Tamerlan when he returned from Russia's Dagestan region in 2012, due to a spelling error.
Though Tamerlan had triggered a terrorism alert at New York's JFK airport, he was not arrested or questioned because his name was spelt wrongly on the immigration checklist, NBC News had reported.
The latest report was produced by the inspectors-general of various national security establishments in the US. The findings, which have not been made public, will be reviewed by the members of Congress on Thursday, NYT said.