The NYPD is stepping up security in Brooklyn as police officers around the city continue to receive threats.

The news comes after two officers, Rafael Ramos and Wenjein Liu, were shot and killed in Bed-Stuy.

Security was upped at the 79th and 81st precincts.

The NYPD released a statement saying all threats are taken seriously.

The NYPD says it has assessed hundreds of online postings, calls to 911 and calls to 311 that have resulted in about 40 threat investigations. 

It says about half of the investigations have been closed or referred to other agencies, and it has made four arrests.

The NYPD urges officers to remain vigilant at all times.

On Tuesday, a source told News 12 that there was a bomb threat called into the 75th Precinct. Officers blocked off the street while they investigated, but they eventually reopened the street Wednesday.

Also on Tuesday, the words "kill cops" were spray painted onto the sidewalk near the 88th Precinct in Clinton Hill. Police were on scene, though there is no word on any suspects.