Details added (the first version was posted at 10:42)
Explosions and gunfire is heard in Boston, where a massive police hunt is underway for a gunman who killed a police officer at the campus of the Massachusetts Institute of Technology (MIT), RIA Novosti reported with reference to France-Presse.
On Friday a gunman shot dead a police officer, ensuring guarding of the building. According to local media outlets, police cordoned-off the scene. Search is underway for the gunman.