People have begun to leave tributes at a makeshift memorial at the scene where two police officers were shot dead in New York.
New York mayor Bill de Blasio has described the shooting of two New York City police officers yesterday as an 'execution style' killing.
Speaking today, as he ordered flags flown at half mast around the city as a mark of respect, de Blasio said: "Although we're still learning the details, it's clear that this was an assassination, that these officers were shot execution style."
Officers Rafael Ramos, 40, and Wenjian Liu, 32, were shot by 28-year-old Ismaaiyl Brinsley who then fled into a nearby underground station before killing himself.
The man suspected of shooting dead two New York police officers yesterday posted a message on his Instagram account before the incident warning of his plans.
Ismaaiyl Brinsley posted: "I'm putting wings on pigs today. They take 1 of ours, let's take 2 of theirs," using the hashtags Shootthepolice RIPErivGardner (sic) RIPMikeBrown.
New York police chief Bill Bratton said that Brinsley shot and wounded his ex-girlfriend earlier in the city Baltimore and made posts from her Instagram account.
The shooting happened hours after his "pigs" post, around the time that Mr Bratton said New York police were receiving a warning fax from the authorities in Baltimore.
A silver Semi-automatic pistol has been recovered on a New York subway, the New York Police department said.
It's sometime difficult to find the words to speak to events like those that occurred today, to try and make sense of them. But, we'll try.
While sitting in a marked NYPD police car, in full uniform, both were ambushed and murdered in front of 98 Tompkins Avenue in the Bedford Stuyvesant area of Brooklyn, New York City.
Police Commissioner William J. Bratton wrote in a blog that two of New York's finest were shot and killed "with no warning, no provocation".
A White House official has said that Barack Obama was briefed on the fatal shootings of two New York police officers.
The US President was informed of the shootings while playing golf in Kailua, Hawaii, where he is vacationing for two weeks with his family.
White House staff are continuing to monitor the situation, the official said.
President Barack Obama has condemned the murder of two police officers in New York.
The two officers, Rafael Ramos and Wenjian Liu, were shot by 28-year-old Ismaaiyl Brinsley who then killed himself.
President Barack Obama said "two brave men won't be going home to their loved ones tonight", and "for that, there is no justification".
He added that police officers "deserve our respect and gratitude every single day".
The NYPD has released photographs of the two police officers who were "assassinated" by a gunman as they sat in a patrol car.
Officers Wenjian Liu,32, and Rafael Ramos, 40, were shot by 28-year-old Ismaaiyl Brinsley who then fled into a nearby underground station before killing himself.
There is no sign at this point of any connection to the killing of two New York police officers to terrorism, police commissioner William Bratton said in a press conference.
The two New York police officers who were shot and killed in their patrol car have been named as Officers Wenjian Liu and Rafael Ramos by the NYPD commissioner.
"They were quite simply assassinated," William Bratton told reporters at a press conference.
The suspect, who fled to a nearby underground station before shooting himself, has been identified as 28-year-old Ismaaiyl Brinsley.
Brinsley also shot and seriously wounded his girlfriend in the city of Baltimore earlier in the day before coming to New York, the commissioner said.
The man who shot and killed two New York police officers as they sat in their patrol car may have been seeking retribution against law enforcement, it has been reported.
According to NBC News, the man posted several threatening messages on the social media network Instagram.
The police deaths in Brooklyn followed weeks of protests in New York and other parts of the United States after separate cases in which grand juries declined to charge two white police officers involved in the deaths of two unarmed black men.