New York City Police are responding to a new video message from Islamic State extremists, which urged lone wolf supporters to “rise up”.
The NYPD's deputy commissioner of intelligence and counterterrorism John Miller said the video was something that authorities had to take “very seriously without overreacting”.
"It is something of concern,” he said.
“We put out a city wide notice to police officers last night asking them to take extra care."
Lone wolf attacks are difficult to predict and surveillance can be fraught.
Australia, which just had its own brush with terror, is expected to have a representative at a terrorism summit announced by the White House.
It is not known yet if Prime Minister Tony Abbott will attend the summit, set down for February 18, which will look at the how the world can fight violent extremism.
Authorities are hoping for answers into the review of last month's Sydney Lindt cafe siege.
Terrorism expert Greg Barton said there are “dozens of people of concern” in Australia, “any one of which or perhaps even someone we don't know may do something”.
