Supt. Marlene Snowman said officers were continuing to search for the shooter, more than 16 hours after a manhunt began.
Snowman said the suspect is carrying high-powered firearms.
Commanding Officer Roger Brown said the most recent sighting of the suspect was just after daylight Thursday and they were able to positively identify him.
Snowman said they were unable to confirm his identity on two other occasions when he might have been sighted.
Brown said police officers from across the country have been brought in to help arrest the suspect.
The RCMP were searching for 24-year-old Justin Bourque, a Moncton man who was wearing military camouflage and carrying two rifles in a picture of him released by police on Twitter on Wednesday night.
Residents in the area where police were searching have been urged to stay inside their homes and lock their doors.
The RCMP released a map of a large swath of the northwest section of the city, including a heavily wooded area, where they wanted people to remain inside.
Schools and government offices were closed, and city buses were pulled off the roads.
The Mounties have said the two wounded officers suffered non life-threatening injuries.
MONCTON, N.B. - An RCMP manhunt for a gunman suspected of killing three Mounties and wounding two others passed the 12-hour mark today in Moncton as a large section of the New Brunswick city was under a virtual siege.
Heavily armed RCMP officers patrolled the small city overnight in the search for 24-year-old Justin Bourque, a Moncton man who was wearing military camouflage and carrying two rifles in a picture of him released by police on Twitter.
Late Wednesday, the RCMP in New Brunswick tweeted a photo of the suspect, who they said was armed and dangerous. They urged anyone with information on his whereabouts to call 911.
The two injured officers were being treated for wounds that the RCMP described as non life-threatening.
The RCMP released a map of a large portion of the northwest section of the city, including a heavily wooded area, where they wanted people to remain inside with their doors locked.
They warned people to expect roadblocks and traffic disruptions. Schools and government offices were closed, and the city pulled its buses off the roads.
The RCMP have scheduled a news conference for 10:45 a.m. today to provide an update on the manhunt.
Late Wednesday night, Const. Damien Theriault broke down in tears at a media briefing as he spoke of the deaths of his three colleagues.
"We are professionals," Theriault said. "We will ensure the security of the public. We are going to do that."
He said police believed the suspect was at large in the Pinehurst subdivision area of the city early on Thursday morning. Police first responded at 7:30 p.m. Wednesday, he said.
Daniel St. Louis, a commercial photographer in Moncton, was among the first on the scene Tuesday around 8:30 p.m. when he came across two police vehicles on different streets with blood visible inside.
He said no one was around, except for a few curious neighbours peeking through their front doors.
One of the vehicles, a marked police cruiser, was surrounded by shattered glass. The other, an unmarked SUV with its lights still on and the driver's side door left open, had several bullet holes through its front windshield.
St. Louis said he saw something shortly after that will always haunt him.
"I walked over and I saw two feet, facing the street, toes up," said St. Louis, 51. "I realized, 'Oh my God. There's somebody down.' As I got close, I realized it was an officer and this is not a good situation."
St. Louis said he doesn't know what to make of the tragedy unfolding in the city of about 69,000.
"Our quiet little city, what is going on here?" he said. "How is this happening to us? It always happens to somebody else."
Danny Leblanc, 42, said he saw the shooter in the distance Wednesday evening, wearing a camouflage outfit and standing in the middle of the street with a gun pointed at police cars.
The construction worker said he believed it was an RCMP officer until he heard a burst of automatic gunfire coming from the man's gun.
"That guy was standing on the road afterwards and he was looking towards us," he said.
He said he quickly retreated into his home with his family, adding a neighbour posted on social media that a kitchen window was shattered by gunfire.
Leblanc said few people on his normally quiet street were sleeping as they awaited word at midnight on whether arrests had been made.
"It's just crazy," he said.
The deaths of the three officers has shocked the city, he added.
"It's devastating. I don't know if he was on a hunt for them, or what."
Prime Minister Stephen Harper offered his condolences to the families, colleagues and friends of those affected by the shootings.
"We also offer our prayers for the speedy recovery of those injured," he said in a statement.
"This violent incident is a stark reminder that our men and women in law enforcement put their lives on the line in Canada every day to protect our citizens and communities.
"The sacrifice of these brave officers will be honoured and remembered."
Mayor George LeBlanc also offered his condolences to the families of the police officers who were killed and those who were injured.
"It is a terrible tragedy," he said.
"We as a city must pull together as a family to support those who have suffered losses."
Sean Gallacher, who lives near the area where police were concentrating their search, said he heard what he now believes were gunshots but initially thought his daughter had dropped some toys on the floor above him.
"I was downstairs and heard a few bangs," said Gallacher, 35.
"I went to check but she hadn't dropped anything. Then I heard the news and realized what it actually was."
The RCMP confirmed the deaths of the three officers on Twitter at about 11 p.m.
Based on information from the RCMP's Honour Roll page on its website, the last Mountie to die from a gunshot was Const. Douglas Scott on Nov. 5, 2007. He was shot while responding to a call for help involving an impaired driver at Kimmirut, Nunavut.
The most recent police officer killed in the line of duty was Const. Steve Dery of the Kativik police force in northern Quebec. Dery, 27, was shot and killed after he and another constable responded to a domestic violence call on March 2, 2013.
The shootings in Moncton also brought back memories of an RCMP tragedy in Mayerthorpe, Alta., on March 3, 2005, when Constables Anthony Fitzgerald Orion Gordon, Lionide (Leo) Nicholas Johnston, Brock Warren Myrol and Peter Christopher Schiemann were shot and killed.
Officials with the Horizon Health Network said the Moncton Hospital was treating two people who were listed in stable condition. The hospital was placed on Code Orange after the shootings to prepare it to handle multiple casualties as extra staff were brought in.
With files from Michael Tutton in Halifax.