According to the Associated Press, the threat is deemed credible and may involve car bombs targeting bridges and tunnels in New York City or Washington DC.  Officials stress the threat is unconfirmed and the warning was issued out of an abundance of caution.

CNN reports the threat involves three people, one of whom may be a U.S. citizen, and it is not believed that they have entered the country yet.  The information came from a credible source in the tribal area of Pakistan, near the Afghanistan border.

New York City Mayor Michael Bloomberg and police commissioner Raymond Kelly held a press conference Thursday night to address the threat.  Kelly said citizens should expect to see vehicle checkpoints around the city as well as increased security on subways.

“The best thing we can do to fight terror is to not let it intimidate us,” Bloomberg said.