NYPD alerted of 'credible' threat toward officers after last week's 'assassination attempt' The warning comes after a weekend in which multiple officers were shot.

The New York City Police Department is warning officers to be "vigilant and alert" following increased "credible" threats toward its officers. Officials are advising all officers to have a heightened awareness "in light of the events that transpired over the past weekend in the Bronx."

Officials sent a department-wide email stressing there are "no specific threats against the department," but said desk officers must ensure that every station house security post is assigned and staffed at all times.

Law enforcement sources tell ABC News that federal authorities notified the NYPD that they took an alleged MS-13 member in custody that they believe had made threats against police officers in the Bronx and in other parts of the city.

NYPD had no comment, other to say they have no one in custody in connection to any threats.

The NYPD security note comes on the heels of a violent weekend that saw multiple officers targeted in what the city called a "premeditated assassination attempt," allegedly by the same person.

Police said 45-year-old Robert Williams walked up to a marked police van, asked for directions, and then opened fire on the evening of Feb. 8. Officer Paul Stroffolino, who was struck by a bullet in the neck and chin during the incident, was taken to a local hospital by his partner after putting the car into drive once he saw the suspect's gun.

Around 8 a.m. the following morning, Williams allegedly walked into the 41st Precinct, not too far the previous night's police shooting, and opened fire at officers and a civilian employee, hitting Lt. Jose Gautreaux in the arm, according to the police.

Officers arrested Williams after he ran out of bullets, police said. He now faces 14 attempted murder charges.

Williams will be in court again on Friday at 9:30 a.m. ET.

"It's only by the grace of God and the heroic actions of those inside the building that took [the suspect] into custody that we are not talking about police officers murdered inside a New York City Police precinct," NYPD Police Commissioner Dermot Shea said during a press conference.

Both Gautreaux and Stroffolino have been released from the hospital.

"It was a quiet Sunday morning when bullets started flying inside the 41st Precinct. Our officers handled it with heroism and extraordinary skill, showing the true caliber of the men and women who serve in the NYPD," New York City Mayor Bill de Blasio said Sunday. "Thank God our officers are alive … This was a premeditated assassination attempt against New York's Finest. It was also an attack on ALL New Yorkers and everything we believe in."

Following last weekend's shootings, the Sergeants Benevolent Association, without providing evidence, blamed de Blasio for the attacks and what they said was an increase in negative public sentiment toward law enforcement officers.

"Mayor DeBlasio [sic], the members of the NYPD are declaring war on you," the SBA tweeted. "We do not respect you, DO NOT visit us in hospitals. You sold the NYPD to the vile creatures, the 1% who hate cops but vote for you. NYPD cops have been assassinated because of you. This isn't over, Game on!"

Freddi Goldstein, a spokeswoman for de Blasio, called the statement from the SBA "absolutely reprehensible."

ABC News' Ivan Pereira contributed to this report.