Two New York police officers were shot dead in their patrol car  afternoon by a gunman who claimed that he was angered by two recent racially-charged controversies.

Rafael Ramos and Wenjian Liu were shot dead in their car while working overtime in the East Flatbush neighbourhood of Brooklyn, Xinhua quoted New York Police Commissioner William Bratton as saying.

The two officers were rushed to Woodhull Medical Centre, where they were declared dead. Dozens of colleagues joined their families at the hospital in a show of support.

Ramos, father of a 13-year-old boy, was two months away from his 40th birthday. Liu, 32, got married only two months ago.

The two officers were “shot and killed with no warning, no provocation”, and they were “quite simply, assassinated”, said Bratton.

Citing witness, he said the suspect, identified as Ismaaiyl Brinsley, approached the police car without saying a word and, taking a shooter’s stance on the passenger side, opened fire into the front passenger-side window with a handgun.

The 28-year-old black man, who had addresses in Georgia and Brooklyn, then fled into the subway and engaged with the police before shooting himself dead, added the commissioner.

Brinsley was a fugitive who had a long record of crimes and had murdered his girlfriend in Baltimore Saturday morning, media reports said.

The tragedy came in the wake of nationwide protests triggered by the decision of a grand jury not to indict the policeman who killed an unarmed black young man named Michael Brown in Ferguson, Missouri.

The tension was exacerbated later by the non-indictment decision of a New York grand jury in a similar case, which involved the chokehold death of black vendor Eric Garner.

Prior to the attack, Brinsley claimed on social media that he was enraged by the Brown and Garner cases and intended to kill police officers in revenge.

However, Bratton said the linkage between Brinsley and the anti-police protests was under investigation.

US President Barack Obama condemned the shooting in a statement.

“I unconditionally condemn today’s murder of two police officers in New York City … Tonight, I ask people to reject violence and words that harm, and turn to words that heal,” said Obama.