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In the wake of the Belgium terror attack, the NYPD has issued an internal memo to all cops urging them to stay alert.

"When more than one officer is at a specific location, all officers must work together to constantly monitor each other's immediate vicinity for any possible safety threat," reads the alert transmitted about 5 p.m. Tuesday.

The attack in Liege left two police officers and a civilian dead. Two other Liege cops were wounded.

Cops in New York have been instructed to watch a video called "Tactical Awareness" sent Tuesday to all officers’ cell phones.

On Wednesday, Chief of Patrol Rodney Harrison visited precinct roll calls around the city to remind cops to be on the alert.

The Liege terrorist deliberately targeted the police. He repeatedly stabbed two officers from behind and then shot them in the back of the head.

He shouted “Allahu Akbar” (God is great) during the encounter.

The civilian who died was sitting in a nearby car and was struck by bullets.

The killer ran into a school, briefly taking a janitor hostage, before running outside again.

He then engaged in a shootout with more cops. He wounded two of them before he was shot dead.

“Police were definitely the target of this attack,” Liege Mayor Willy Demeyer said.

NYPD officials do not believe an attack is imminent but want cops to be on their guard.

“While there are currently no specific threats against members of the NYPD, given the tragic and deliberate severity of this attack, it is imperative that all members maintain strong situational awareness,” the alert sent Tuesday reads.