More chaos and violence erupted near Boston late Thursday night as two young men armed with multiple guns and explosives engaged in a long, violent standoff with police, FBI and homeland security officers in Watertown, Mass., according to the Boston Globe.

Authorities say those two young men are the suspects in Monday's Boston Marathon bombings, and the Boston Police Department reported one suspect had been captured. Another remains on the loose in Watertown. State police also say they are after the second suspect and no arrest has been made, according to WCBV breaking reports. Authorities have established a 20-block perimeter as they continue the search.

A hail of gunfire and sirens descended on Cambridge and Watertown late Thursday night and early Friday morning, when an MIT police officer was shot and killed, and a carjacking led police on a chase into the Watertown area.

Witnesses tweeted sounds of explosions, SWAT cars and hundred of police officers emerging to the scene. Officers were screaming about improvised explosive devices left in backpacks, according to the Boston Globe.

FBI agents were also on the scene.

“We are aware of the situation, we are being involved, and we are monitoring,” said an FBI representative who requested anonymity because of not being authorized to speak publicly. The FBI source said early Friday it is “too early to speculate” on a relation to the Marathon bombing.

Police have released new, more detailed images of the suspects.