Russia tipped off the FBI about Boston Marathon bombing suspect Tamerlan Tsarnaev twice in 2011, US officials told Reuters.
The second warning raised questions about whether the FBI and CIA failed to share information.
Republican senator and member of the Senate Intelligence Committee Dan Coats said: "That's something that we have to look at.
"That's one of the key things that we have learned and need to work on to make sure it doesn't happen again, and that is simultaneous communication to all the relevant agencies when a warning is posted."
In a briefing to a House of Representatives panel, US investigators said the two suspects apparently became radicalised by information on the internet.
More top news
Liam Payne's outburst came after X Factor judge Louis Walsh criticised a reporter over a question about Payne's girlfriend Cheryl.
Spotting the warning signs for the many private causes of self-harm can be hard in the era of social media. Here's what you can do to help.
An "institutional conspiracy" on an "unprecedented scale" existed in Russia to help some 1000 of its athletes benefit from doping.