A gunman was shot dead and three discovery staff members were led to safety by the police ending hours of standoff after a man had taken them as hostages at the Discovery Channel headquarters in the suburb of Silver Spring.

The gunman carried explosive devices on his back as he was against the programmes shown by the channel, police said and identified him as James Lee.

The hostages were rescued unhurt during the standoff. It all began around 1 pm, when Lee entered the building and appeared to have bomb strapped to his chest, they said.

The gunman took them hostage and asked others not to leave the building.

Immediately the police cordoned off the area and evacuated the building. Around 100 children in the daycare centre of the building were safely moved to a nearby location. Police, who started negotiations with Lee, said that he demanded that the Discovery Channel "must broadcast to the world their commitment to save the planet".

Montgomery County Police chief J. Thomas Manger said that as the suspect pulled out a handgun and pointed it at one of the hostages our tactical units moved in and shot the suspect.