Police in New York and other major U.S. cities are on alert after the Islamic State made a threat over the weekend to target soldiers, law enforcement officials and civilians in America.

Officials say that ISIS posted a video on Twitter Saturday that called for its followers to stage attacks on police officers and soldiers in the U.S., along with Canada, Great Britain and France, CBS New York reports. The video features a message that was originally posted in Sept. 2014 that tells followers to "rise up and kill intelligence officers, police officers, soldiers, and civilians."

Following the threat, the New York Police Department received an internal memo, warning cops to "remain alert and consider tactics at all times while on patrol," reports CNN.

According to John Miller, the NYPD's deputy commissioner of intelligence and counterterrorism, the NYPD notified police officers of the message and advised them to be "extra vigilant."

"Pay attention to your surroundings and pay close attention to approaching vehicles," part of the memo reads, according to CBS New York. "Pay close attention to people as they approach and look at their hands."

The NYPD also responded to the threat by adding increased security and extra K-9 units and emergency service units at key locations in the city, including Times Square.

The department is on a "heightened security posture on a normal day compared to almost any other police department," Miller said.

FBI agents and the U.S. Department of Homeland Security issued a similar bulletin to law enforcement across the nation.

Police Commissioner Bill Bratton spoke out about the threats on Monday, telling "CBS This Morning" that the NYPD is taking the threats very seriously.

"There are a number of people who are in the process of being radicalized," he said. "Something like this can be the last straw to move them forward. Additionally, they are continually working to attract new recruits."

Mayor Bill de Blasio also reassured New Yorkers that the NYPD is doing all they can to keep the city safe.

"There is no down day, there is no day when we're less vigilant, we're vigilant every day," de Blasio said. "We have 1,000 counterterrorism officers who do extraordinary work, but when a tragedy like this occurs we reinforce additionally any location we believe to be sensitive."

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