New York: Two New York police officers were shot and killed at point-blank range in their patrol car here by a man with an apparent grudge who later committed suicide with the same gun, officials said, amid weeks of nation-wide protests over police killings of unarmed black men.

The slain officers were identified as Wenjin Liu, a seven-year veteran of the NYPD, and Raphael Ramos, who joined the force two years ago.

The 28-year-old gunman was identified as Ismaaiyl Brinsley, a black man, who had driven over 300 km from Baltimore. Authorities said he had written in social media posts that he planned to kill police officers in the wake of the deaths of two blacks, Eric Garner and Michael Brown, by police officers.

"Although we're still learning the details, it's clear that this was an assassination, that these officers were shot execution style," said New York Mayor Bill de Blasio.

"Our city is in mourning. Our hearts are heavy," he said at a press conference on yesterday's killings.

"Our entire city was attacked by this heinous individual," the mayor said.