US President Barack Obama says no stone will be left unturned in reviewing whether any sensitive intelligence was missed that could have stopped the deadly attacks on the Boston Marathon.
Obama called it "standard procedure," but said the review, which will last only 90 days, would help determine if all the information was shared properly.
Brothers Dzhokhar and Tamerlan Tsarnaev are accused of using a weapon of mass destruction during the April 15 marathon. Three people were killed and more than 260 injured when two bombs exploded near the finish line.
"Based on what I've seen so far, the FBI performed its duties, the Department of Homeland Security did what it was supposed to be doing," Obama told a White House news conference, describing how the FBI interviewed Tamerlan Tsarnaev, who died in an escape attempt.
But the president said it would help determine whether "there were additional things that could have been done."
Shawn Turner, a spokesman for the Director of National Intelligence James Clapper, said the review is limited to how information about the suspects was handled before the attack because the investigation of the bombing is still ongoing. He added that Clapper believes his agencies shared information appropriately.
The review will be conducted by I. Charles McCullough III, the independent intelligence community inspector general, which is a position that is Senate-confirmed and is authorized to reach into any US intelligence agency to conduct reviews.
Lawmakers have suggested that an intelligence breakdown may have contributed to the attacks.
"Just because the FBI didn't find derogatory information about the suspects doesn't mean it wasn't there to be found," said Democratic Rep. Adam Schiff, a member of the House intelligence committee. "But nor should we leap to a conclusion of malfeasance. Instead this review may produce one important component of the 'lessons learned' from the attacks," he added Tuesday.
The review was first reported by The Boston Globe.
Obama also said the security review following the bombings will look at whether there is more the government can do to stop people within the US who might become radicalised and plan terror attacks.
One of the dangers the US faces now, Obama said, is people who might decide to attack because of "whatever warped, twisted ideas they may have."
Obama's news conference came a day after a judge approved the appointment of death penalty expert Judy Clarke to defend 19-year-old Tsarnaev. But judge Marianne Bowler denied, at least for now, a request from Tsarnaev's public defender, Miriam Conrad, to appoint a second death penalty lawyer - David Bruck, a professor at Washington and Lee University School of Law.
Tsarnaev's lawyers could renew their motion to appoint another death penalty expert if he is indicted, the judge said.
Clarke's clients have included the Unabomber, Ted Kaczynski, who killed three people and injured 23 during a nationwide bombing spree between 1978 and 1995; Susan Smith, a woman who famously drowned her two children; Atlanta Olympics bomber Eric Rudolph; and most recently Jared Loughner, who shot former Rep. Gabrielle Giffords in the head. All received life sentences instead of the death penalty.
Obama said the US and Russia are overcoming Cold War era suspicions to co-operate on the investigation of the Boston Marathon bombings as his top diplomat announced plans to travel to Russia.
Obama acknowledged that suspicions still exist. But he added that Russian President Vladimir Putin has assured him that Russia is committed to help and that the two sides are looking for ways to improve counterterrorism co-operation more broadly.
"Obviously old habits die hard," he said.
Meanwhile, Secretary of State John Kerry is headed to Russia next week to meet Putin and Foreign Minister Sergey Lavrov. The talks are expected to touch on the attack in Boston and a host of bilateral tensions. The US and Russia are at odds on Syria, Iran and missile defense among other issues. Tensions have also spiked over the Kremlin's halt on US adoptions of Russian children and new Russian restrictions on civil society groups.
Kerry told reporters today his upcoming trip to Russia is "overdue."
Russia's co-operation in the Boston investigation is key, because the suspected bombers are Russian natives who immigrated to the US. Russian authorities warned U.S. officials before the bombings that they had concerns about the family.
The April 15 bombings at the Boston Marathon killed three people and injured more than 260.