BOSTON - Police said an incident at the JFK Library in Boston is now believed to have been a fire, after the police commissioner said at a press briefing it was an explosion.

Commissioner Ed Davis told reporters just before 4 p.m. CT they were treating the incident at the library at that time as if it were related to two other explosions at the Boston Marathon.

"We are not certain that these incidents are related, but we are treating them as if they are," Davis said.

Boston Police later posted to their Twitter account the library incident "appears to be fire related."

Police earlier said on Twitter that 23 were injured and 2 dead after the explosions at the marathon. The Boston Globe later reported the number of injured had risen above 100. Davis did not confirm any casualty numbers at the press conference.

Davis also said no other explosive devices have been found by investigators at that time. He said many people dropped bags or parcels as they left the race course, and explosives teams were treating all of those as suspicious packages, including possibly blowing them up.

He also asked people not to gather outside in large crowds while police investigate the explosions, and send in any tips or video from the scene to authorities.