New York City is on high alert for a potential attack from the Islamic State militant group days after terrorist attacks in Paris that resulted in at least 20 deaths and a three-day manhunt that saw the international city gripped by violence. The New York City Police Department is allegedly investigating repeated threats from the militant group also known as ISIS after the release of a message that urged followers to "rise up and kill intelligence officers, police officers, soldiers and civilians."

The threats singled out the U.S., France, Australia and Canada as targets, according to CNN. The FBI and U.S. Department of Homeland Security reportedly have issued similar warnings to law enforcement agencies across the nation. At the same time, Attorney General Eric Holder said Sunday that the possibility of a similar attack unfolding in the U.S. after the Paris massacre targeting the satirical magazine Charlie Hebdo keeps him "up at night."

"I certainly think that the possibility of such attacks exists in the United States," Holder told CBS' "Face the Nation" on Sunday. "It is something that we worry about all the time. It is something that we meet about all the time."

Holder later told CNN's "State of the Union," according to The Hill: "What we saw in France over the course of this last week is unfortunately what we're going to have to confront in the future. We've seen these kinds of attempts in the United States … This is the nature of the new threat we must confront."

The Charlie Hebdo attacks began Wednesday in Paris when at least two suspects raided the magazine's office and killed 12, including two policemen. An alleged accomplice later attacked a kosher supermarket in Paris on Friday, resulting in more deaths.

U.S. lawmakers also warned about potential terrorist attacks after the Charlie Hebdo shootings. Senate Intelligence Committee Chairman Richard Burr, R-N.C., described the mounting terrorist threat around the world as a "war on Western civilization." 

The Paris attacks have helped shape an ongoing debate over funding of the Department of Homeland Security, which oversees border security. Republicans have threatened to reduce funding to DHS because of President Barack Obama's immigration policies, but some critics of that plan said lawmakers shouldn't threaten national security at a time when Islamist terrorists have their sights set on the U.S.

“As the risk of terrorism rises, this perilous Republican tactic sends the worst possible message at a very dangerous time,” Drew Hammill, a spokesman for House Minority Leader Nancy Pelosi, D-Calif., said in a statement Friday, according to Fusion.