Two New York City police officers who were ambushed and shot dead in their vehicle were "quite simply, assassinated", and the suspect had earlier made Instagram posts that were very anti-police, Police Commissioner William Bratton said.

Bratton said the officers, Wenjian Liu and Rafael Ramos, were shot in the head without warning on Saturday when a gunman approached the passenger window of a marked police car and opened fire.

The suspect, 28-year-old Ismaaiyl Brinsley, then ran inside a Brooklyn subway station and fatally shot himself in the head. Brinsley was black; the officers were Asian and Hispanic, police said.

Bratton said the suspect had shot and wounded his ex-girlfriend earlier on Saturday in Baltimore and made posts from her Instagram account.

"This may be my final post," said one that included an image of a silver handgun. The post had more than 200 likes.

Two officials said that the suspect posted about shooting two "pigs" in retaliation for the death of Eric Garner: "I'm putting wings on pigs today. They take 1 of ours, let's take 2 of theirs." He used the hashtags Shootthepolice RIPErivGardner (sic) RIPMikeBrown. The officials spoke on condition of anonymity because they were not authorized to speak publicly.

The shooting occurred hours later, around the time that Bratton said New York police were receiving a warning fax from Baltimore authorities.

US Attorney General Eric Holder called Saturday's shooting deaths an "unspeakable act of barbarism".

President Barack Obama, in a statement issued on Saturday while he is vacationing in Hawaii, said: "I unconditionally condemn today's murder of two police officers in New York City. Two brave men won't be going home to their loved ones tonight, and for that, there is no justification ... I ask people to reject violence and words that harm, and turn to words that heal."

Officers in the New York Police Department are being criticized for their tactics following the recent chokehold death of Eric Garner, an unarmed black man who was stopped by police on suspicion of selling loose, untaxed cigarettes.

Demonstrators across the country have staged protests since a grand jury decided on Dec 3 not to indict the officer in Garner's death. The decision closely followed a Missouri grand jury's decision not to indict a white officer in the fatal shooting of Michael Brown, an unarmed black 18-year-old.

The Rev Al Sharpton, a civil rights activist, said Garner's family had no connection to the suspect and denounced the violence.

"Any use of the names of Eric Garner and Michael Brown in connection with any violence or killing of police, is reprehensible and against the pursuit of justice in both cases," Sharpton said.

AP - AFP

(China Daily 12/22/2014 page12)