-- Cities have stepped up security after the attacks, including Washington, New York, Miami, Chicago, Atlanta and Los Angeles.
-- British police said they are reviewing the security plan for the London Marathon scheduled for Sunday. The marathon will observe 30 seconds of silence and is urging runners to wear a black ribbon to mark the Boston tragedy.
-- "Boston is not going to be intimidated by this," said Secretary of State John Kerry, a former U.S. senator from Massachusetts. "But we are going to find out who did this. The police work being done is extraordinary. The FBI is remarkable. There is a great deal of forensic evidence. We are hopeful we can bring people to justice."
"The Islamic Republic condemns killing of innocent people in U.S. Boston, Pakistan, Afghanistan, Iraq and Syria in equal measure," Iran's Ayatollah Ali Khamenei said Wednesday, according to a report on state-run Press TV.
-- Obama and first lady Michelle Obama will travel to Boston on Thursday for an 11 a.m. interfaith service dedicated to the victims. The president is expected to meet with the families of those wounded or killed.
--Obama declared an emergency in Massachusetts and ordered federal aid to supplement state and local response efforts.