A former Army medic says the scene at Monday's Boston Marathon was "more like Baghdad and Bombay than Boston."
Bruce Mendelsohn was attending a post-race party in an office building just above the blast site when an explosion knocked him to the floor. He rushed outside and found blood, glass and debris everywhere, and began applying pressure to what he calls "gruesome" wounds.
One of the runners describes a gruesome scene inside a medical tent near the finish line, as bombing victims were brought in "with no limbs." He says he tried to shield his children's eyes, but says "they saw a lot."
At least three people were killed and more than 140 injured, including at least 17 critically, when two bombs exploded almost simultaneously about 100 yards apart.
Security is being tightened at landmarks, government buildings, transit hubs and sporting events around the U.S. and the world following the explosions at the Boston Marathon.
In New York, authorities deployed critical response teams, highly visible patrol units that move in packs with lights and sirens, along with more than 1,000 counter-terrorism officers.
Highly trafficked areas like the Empire State building, the United Nations and the World Trade Center site were being especially monitored.
At the White House, the Secret Service expanded its security perimeter after the attacks, shutting down Pennsylvania Avenue and cordoning off the area with yellow police tape.
Several Secret Service patrol cars have blocked off entry points, although the White House was not on lock-down and tourists and other onlookers were still allowed in the park across the street.
And the worries are reverberating across the Atlantic. An already robust security operation is being beefed up for Wednesday's funeral of former Prime Minister Margaret Thatcher in Britain, where police are also reviewing security plans for Sunday's London Marathon.