New York City Mayor Michael Bloomberg said he did not feel threatened or angry after two anonymous letters, believed to be carrying the deadly poison ricin, were sent to him.
The letters threatened Mayor Bloomberg and referred to the debate on gun control, according to police.
Mr Bloomberg has been one of the country's most visible gun control advocates since the shooting of 20 young children and six adults at a Connecticut school
When asked whether he was angry about the letters, he said: "No I'm not angry. There are people who I would argue do things that may be irrational, do things that are wrong. But it's a very complex world out there. And you just have to deal with them."
New York Mayor Michael Bloomberg has said that 1,000 NYPD officers have been assigned to counter-terrorism duties in the wake of the Boston explosions. A statement from his office said:
I have spoken with Police Commissioner Ray Kelly, and the NYPD has stepped up security at strategic locations and critical infrastructure, including our subways.
Some of the security steps we are taking may be noticeable, including deployment of Critical Response Vehicles and additional police personnel, and others will not be.
We have 1,000 members of the NYPD assigned to counter-terrorism duties, and they - along with the entire NYPD and the investments we have made in counter-terrorism infrastructure - are being fully mobilized to protect our city.