Last Updated Dec 24, 2014 6:00 PM EST
NEW YORK -- New York City police have increased security at some stationhouses and have arrested at least four people over threats to police after the deadly shootings of two officers last weekend.
The NYPD is looking into the threats that prompted the department to station Emergency Services Unit officers at two Brooklyn precincts starting Tuesday.
The Sergeants Benevolent Association tweeted late Tuesday night that the threat came from a confidential informant who said a Baltimore street gang called the Black Guerrilla Family planned to storm the precincts for a shootout with police, CBS New York reported.
On Tuesday, the 75th and 104th precincts in Queens received telephone bomb threats, according to CBS New York. Both buildings were swept by the bomb squad and cleared.
Police on Wednesday wouldn't detail the threats, but said it is advising officers to remain vigilant at all times and that all threats would be taken seriously and investigated immediately.
NYPD commissioner Bill Bratton has ordered officers to work in pairs as a precaution and auxiliary patrols, which involve officers who do not carry weapons, have been cancelled.
In another tweet Tuesday, the SBA warned officers to "Carry your firearm at all times on duty & off, carry addtional (sic) mags & second weapons. Stay in pairs & be vigilant to people around you."
Patrolmen's Benevolent Association President Patrick Lynch sent out an email to members reminding them they are potential target and asking them to always wear their bullet-proof vests and carry a backup gun, CBS radio station 1010 WINS reported.
In addition to the threats, police have increased security at precincts throughout the city to prevent acts of vandalism, such as loosening lug nuts on the tires of squad cars, and other acts that may endanger the lives of cops, sources told CBS New York.
Police said the security measures "will be assessed and police resources will be deployed accordingly."
Meanwhile, an 18-year-old was facing charges of making a terroristic threat after authorities said he put up a menacing photo and message online on Saturday hours after the afternoon ambush of Officers Wenjian Liu and Rafael Ramos by a gunman who had signaled his plans on social media.
Teenager Devon Coley posted a photo on his Facebook page Saturday night of a gunman shooting at a patrol car, symbols showing a gun pointed at an officer's head and a caption with his local precinct's number and "next," according to a court complaint.
His lawyer, Daniel Ades, said Wednesday that the state terroristic-threats law was being misapplied.
"Nobody's condoning threats against police," he said, but "even if this is proven, it doesn't amount to a crime." He noted that the law requires a "reasonable expectation or fear" that a threat meant to influence government or intimidate the public is about to be carried out.
Prosecutors sought $250,000 bail for Coley, who was already facing unrelated gun possession and other charges, the New York Post reported. Court records show a judge released him without bail on the threats charge.
Officials said they had assessed hundreds of online postings and calls to emergency lines, initiating about 40 threat probes, with about half of those being closed or referred to other agencies.
The police department said one 52-year-old man had been arrested after walking into a Manhattan stationhouse and saying: "If I punch you in the face, how much time will I get?" and refusing to leave.
In addition, two Staten Island residents were arrested in separate incidents on Tuesday. A 16-year-old was arrested on a charge of making a terrorist threat and a 46-year-old man was charged with making a false report.
Mayor Bill de Blasio denounced the various threats Wednesday and said the city "will protect the men and women who protect us."
"New York City stands with our police officers in this time of tragedy, as we do every day, and our city will not be intimidated by those spouting hateful, violent messages," he said in a statement.
Police departments around the country were on high alert following the killings. In Colorado, a 33-year-old military veteran was arrested Monday for posting online threats calling for the killing of current and former police officers under the name "Vets Hunting Cops."
And in Northern California, presidents of the three biggest Northern California police unions warned that recent anti-police sentiments are threatening officers' safety.
Recent demonstrations against police brutality have devolved into tasteless vilification of officers, including chants calling for dead police officers, the union heads said in a letter posted online Tuesday.