President Obama defended the FBI's handling of deceased Boston Marathon bombing suspect Tamerlan Tsarnaev in an interview Friday, after some Republican lawmakers have charged the nation's intelligence and law enforcement agencies failed to coordinate their investigations.

"I don’t think it’s fair to say though that law enforcement 'dropped the ball,'" Obama told Univision. "I think that this is a very difficult challenge when you have individuals who are self-radicalizing, they’re not part of some massive conspiracy or a network."

The Central Intelligence Agency allegedly placed Tsarnaev's name into a terror database after being contacted by Russian authorities in 2011, and Republican lawmakers have questioned why that did not trigger a more thorough investigation by the FBI. According to multiple reports, the FBI had already investigated Tsarnaev based on a Russian tip earlier in the year.

Sens. John McCainJohn Sidney McCainGOP strategist donates to Alabama Democrat Meghan McCain knocks Bannon: 'Who the hell are you' to criticize Romney? Dems demand Tillerson end State hiring freeze, consult with Congress MORE (R-Ariz.) and Kelly AyotteKelly Ann AyotteExplaining Democratic victories: It’s gun violence, stupid Trump voter fraud panel member fights back against critics Dems plan to make gun control an issue in Nevada MORE (R-N.H.) have requested a congressional hearing into the administration's handling of the Tsarnaev investigation. Sen. Lindsey GrahamLindsey Olin GrahamGOP and Dems bitterly divided by immigration We are running out of time to protect Dreamers US trade deficit rises on record imports from China MORE (R-S.C.) called for a joint select committee in an interview with CNN on Tuesday.

"When it comes to Boston, we need a joint select committee to look at FBI, the CIA and Homeland Security," Graham said. "The system did not work as designed."

But Obama defended federal officials, saying "the FBI can’t arrest somebody just based on a rumor."

"I mean one of the challenges if we’re going to be an open society, one that respects the law, is that there are going to be times where individuals decide they want to cause harm to people for crazy reasons, for no good reason, for ideological reasons," Obama said. "And if they’re not communicating with a lot of people about their plots, it’s very difficult for law enforcement to find them."

Still, Obama said the administration "can continue to improve and refine how we’re engaging and countering terrorist activity."

"As I said, we’re seeing a review of everything that happened," Obama said. "I will be making sure that we’re following up on any additional improvements that can be made."

The White House said earlier this week that James Clapper, the director of National Intelligence, was organizing an internal revue of the administration's handling of the Tsarnaev tip.