New York Mayor Bill de Blasio said the city "is in mourning" after two police officers were shot execution-style Saturday in their marked car. He condemned the attack as "an assassination" and a "particularly despicable act, which goes against the very heart of our society and our democracy."

The mayor spoke from Woodhull Hospital where Officers Rafael Ramos and Wenjian Liu were pronounced dead earlier in the evening. The suspect, Ismaaiyl Brinsley, allegedly shot the officers in the head as they sat in their vehicle in the Bedford-Stuyvesant neighborhood of Brooklyn. The gunman later shot and killed himself.

"We depend on our police to protect us against forces of criminality and evil. They are a foundation of our society, and when they are attacked, it is an attack on the very concept of decency," de Blasio said. "Therefore, every New Yorker should feel they too were attacked. Our entire city was attacked by this heinous individual."

The police attack comes at an extremely tense moment in New York. Critics of the NYPD accused its officers of racism after Eric Garner, a black man, was killed in July by a white policeman who used an illegal choke hold. Police officers, in turn, say they feel under attack by the community they're tasked with protecting. Both police and civil rights groups have expressed frustration with de Blasio, claiming the mayor hasn't done enough to support their respective sides, the Associated Press reported Friday.

At the Saturday press conference, some police officers turned their backs on the mayor as he walked down a hallway into the main room, cell phone footage indicated.

De Blasio urged the city to join together to support the families of Officers Ramos and Liu. He said he and Police Commissioner William Bratton met earlier with Ramos' wife and 13-year-old son and with Liu's parents and new wife. Together, the leaders and families prayed over the bodies of the fallen officers.

"There is a sadness that is very, very hard to describe," the mayor said.