The NYPD and police across the nation are on alert after threats made by Islamic militants.

Officials say ISIS posted a video on Twitter over the weekend calling for the murder of "intelligence officers, police officers, soldiers and civilians" in the U.S.

The NYPD's top brass sent an internal memo to officers urging them remain vigilant while on patrol.

"For the safety of our officers, we immediately require all foot patrols be assigned in pairs and that there be no solo patrols conducted citywide," said NYPD Commission Bill Bratton. "We also significantly increased security around our station houses."

The NYPD also instructed its officers to keep watch on people who approach them and to look closely at their hands to make sure they're not carrying weapons.

The ISIS video resurfaced just days after the deadly terror attacks in Paris left more than a dozen dead.

The Federal Bureau of Investigation and the U.S. Department of Homeland Security also sent out a joint notification to law enforcement members around the country.

In it, authorities said there is no credible information suggesting an imminent attack in the U.S., but the bulletin stressed to officers, as well as the public, to remain vigilant.