US President Barack Obama on Tuesday defended the FBI from suggestions that it might have prevented the Boston marathon bombing by acting on warnings about one of the suspects.
Russia had advised US authorities about ethnic Chechen Tamerlan Tsarnaev in 2011 and the possibility he was slipping into the grips of hardline Islam, and the FBI probed and interviewed him, although the case was eventually closed.
Tsnarnaev and his younger brother Dzhokhar are accused of going on to carry out the April 15 bombing, which killed three and wounded more than 264 at one of the world's premier sporting events.
But Obama said US authorities had done the best they could in the face of threats that include what he called "self-radicalised individuals".
"Based on what I've seen so far, the FBI performed its duties, the department of homeland security did what it is was supposed to be doing. But this is hard stuff," Obama told a news conference, adding that Russia had been very cooperative in the post-bombing probe.
Still, he acknowledged lingering suspicions between the intelligence and law enforcement agencies of the two former Cold War foes.
"You know, old habits die hard," Obama said.
Tamerlan Tsarnaev died in a shootout with the police as he tried to flee the Boston area three days after the bombing. His younger brother was wounded and captured.