Police are responding to reports that a man with explosives and a gun is holding office workers hostage in Pittsburgh, Pennsylvania.
A Swat team has arrived at the high rise office block in the centre of the city. The road is closed and all traffic is being diverted.
Pittsburgh police are trying to negotiate with the man, who is believed to be holding the hostages on the 16th floor. The man has told police he has a bomb.
The man, who has been identified as Klein Michael Thaxton by police, appears to be updating his Facebook page as he negotiates with police.
He posted earlier that he was "tired of life" and has lost everything. He has as his cover picture a print of Obama, Netanyahu and Ahmadinejad. Other Facebook users are trying to convince Thaxton to hand himself in to police.
No shots have been fired or injuries reported, according to Sky News.