The gunmen involved in a firefight that left six people dead in Jersey City clearly targeted a Jewish market, the mayor said, fuelling suspicions that the bloodshed was an anti-Semitic attack.

Steven Fulop refused to call it an anti-Semitic attack but said surveillance video showed the gunmen driving slowly through the city’s streets and then stopping outside a kosher grocery store, where they calmly got out of their van and immediately opened fire.

Neither the state attorney general, who is running the investigation, nor any other law enforcement authority has confirmed the shooters targeted Jews.

City public safety director James Shea said on Tuesday there was no indication it was terrorism, and police released no immediate information on the killers.

A police officer, three bystanders and the killers all died in the violence on Tuesday afternoon in the city of 270,000 people across the Hudson River from New York City.

The shooting began near a cemetery, where Detective Joseph Seals, a 40-year-old member of a unit devoted to taking illegal guns off the street, was killed while trying to stop “bad guys”, Police Chief Michael Kelly said.

The killers then drove a stolen rental van over a mile to the kosher market, where they used high-powered rifles in a drawn-out battle with police that filled the streets with the sound of heavy gunfire and turned the city into what looked like a war zone, with Swat officers in full tactical gear swarming the neighbourhood.

At the grocery store, police found five bodies — the killers and three people who apparently happened to be there at the time. Police said they were confident the bystanders were shot by the gunmen and not by police.

Two of the victims at the store were identified by members of the Orthodox Jewish community as Mindel Ferencz, who with her husband owned the grocery, and 24-year-old Moshe Deutsch, a rabbinical student from Brooklyn who was shopping there.

Police also removed what they described as a possible “incendiary device” from the van.

Mr Fulop said a review of security camera footage led to the conclusion that the gunmen targeted the market.

“Last night after extensive review of our CCTV system it has now become clear from the cameras that these two individuals targeted the Kosher grocery location,” he tweeted.

At a later news conference, he said the surveillance video shows the van moving slowly and then stopping in front of the store.

“There were multiple other people on the street so there were many other targets available to them that they bypassed to attack that place, so it was clear that was their target and they intended to harm people inside,” he said.

But he cautioned: “I didn’t use the word anti-Semitic’. Anything else is open for investigation.”

Police at the scene
Police at the scene (Eduardo Munoz Alvarez/AP)

Jewish leaders and the Anti-Defamation League, which tracks anti-Semitic attacks, expressed concern about the deaths.

New York mayor Bill de Blasio said on MSNBC that the attack was “clearly a hate crime”, while New York governor Andrew Cuomo pronounced it a “deliberate attack on the Jewish community”.

They announced tighter police protection of synagogues and other Jewish establishments in New York as a precaution.

The kosher grocery is a central fixture in a growing community of Orthodox Jews who have been moving to Jersey City in recent years and settling in what was a mostly black neighbourhood.