FBI Special Agent Richard DesLauriers said the Bureau had identified two suspects in the Boston Marathon bombing investigation.
"The nation is counting on those who have information to come forward and provide it to us," he added.
DesLauriers said investigators regard the suspects as "armed and extremely dangerous," adding that "identifying and locating those responsible is now (our) highest priority."
New photos of the suspects identified by officials as Dzhokar A. Tsarnaev, 19 and Tamerlan Tsarnaev, 26 have been released.
The FBI has released pictures and video of two suspects in the Boston Marathon bombing, seeking the public's help.
President Obama attended a memorial service in Boston today, paying tribute to the victims of Monday's terrorist attack.