A bomb threat prompted the evacuation of the Washington Monument in the U.S. capital Friday afternoon. And in New York, officials are blaming "a prank" for the temporary closure of part of New York's Pennsylvania Station.
The Washington bomb threat was called in to local police at about 2:30 p.m. ET. Though bomb-sniffing dogs moved in and two blocks around the monument were closed off, nothing was found.
A law enforcement official told that the credibility of the threat had been low.
In New York, morning commuters were barred for more than an hour from entering the area where Amtrak commuter trains arrive and depart beneath Madison Square Garden.
After the station was reopened around noon, Amtrak officials said a discarded soft drink bottle -- filled with an unidentified green liquid -- found during the morning rush had prompted the closure.
New York City Police Commissioner Ray Kelly told an afternoon press conference that it appears the security scare was a false alarm.
"In that bottle was a dye and an acid," Kelly said, describing the liquid as "a Draino-type substance."
"It looks like a prank," he added, noting that investigators are now working on their final analysis.
The entire New York City subway system has been on alert since Thursday, when officials warned of a specific threat of an attack on transit network.
Travellers were asked to report any suspicious people or activities, as police searched bags, briefcases and even baby strollers across the sprawling transit system.
The 4.5 million New Yorkers who use the city's subway system could not miss the heavy police presence Friday morning: All of New York's 488 subway stations had at least one uniformed officer stationed either on the platform and, in many cases, guarding each entrance.
Police cruisers, often with their lights flashing, were also parked next to many stations.
But shortly after noon, the police presence largely evaporated. While patrols on the subways themselves continued, CTV reporter David Akin said officers had disappeared from subway station entrances, indicating to travellers that the threat may have eased, CTV reported.