Montrell Jackson was a broken man. Days before he was shot dead by a lone gunman on Sunday morning, the Baton Rouge police officer posted an emotional message on Facebook about the unrest in his home town.

The 32-year-old, named by US media outlets as one of three officers killed following a confrontation with a gunman on the Airline Highway, said he felt "tired physically and emotionally".

"In uniform I get nasty hateful looks and out of uniform some consider me a threat," Mr Jackson said in the July 8 post, accompanied by a photo of him in uniform holding his infant son.

Two days earlier, the fatal police shooting of 37-year-old black man Alton Sterling in Baton Rouge had sparked protests against alleged police brutality against African Americans in cities from Ferguson, Missouri, to Baltimore and New York.

The shooting was captured on video and showed Mr Sterling being pinned to the ground and shot at close range by a white police officer outside a convenience store in the Louisiana capital.

In the days after the shooting, Mr Jackson said he had "experienced so much in my short life and these last three days have tested me to the core".

"I swear to God I love this city but I wonder if this city loves me," he wrote.

"Please don't let hate infect your heart. This city MUST and WILL get better."

He said he had been "disappointed in some family, friends, and officers for some reckless comments but hey what's in your heart is in your heart. I still love you all because hate takes too much energy but I definitely won't be looking at you the same."

He offered support to "any protesters, officers, friends, family or whoever", saying "if you see me [working] and need a hug or want to say a prayer ... I got you".

Three police officers were shot dead and another three wounded by the gunman, who has been identified by US media outlets as Gavin Long of Kansas City, Missouri. Long allegedly carried out the attack on his 29th birthday.

The Los Angeles Times, citing a federal law enforcement official, said Long was a "black separatist". But the publication did not provide any further details.

Police said they received a 911 early on Sunday morning about a "suspicious person walking down the Airline Highway with an assault rifle".

Authorities did not immediately release the names of the dead and wounded, but relatives and friends identified Mr Jackson as among the victims.

"Rest in Peace to my former partner and one of the best cops I've ever known... His name was Montrell Jackson!" Facebook user Marcus Tillman said in a post, which received more than 8000 likes and 6000 shares by midday on Sunday.

"He was a black life that apparently didn't matter to the one that took it!"

Montrell Jackson, an officer killed in #BatonRouge, posted this msg last week. Heartbreaking. RIP.(via @ladyhaja) pic.twitter.com/PhNY9F8EY5— The Undefeated (@TheUndefeated) July 17, 2016

Rest in peace to my cousin Montrell Jackson who was one of the policeman that was killed. #PrayForBatonRouge— Josh Jackson (@joshiejack17) July 17, 2016

Lonnie Jordan, Mr Jackson's father-in-law, described his son-in-law as a "gentle giant" - tall and stout and formidable looking, but with a peaceful disposition, saying he was "always about peace".

A friend, Darnell Murdock, told The Advocate newspaper in Louisiana that Mr Jackson had recently celebrated his 10-year anniversary with the Baton Rouge Police Department. He also had a young son.

"He loved his job," Mr Murdock said.

"It motivated him to go out and change people's lives. He was on [the force] to help people, to make you have a better day.

"He was humble, kind and sweet … He wasn't on there to write tickets. I don't understand how this could happen to someone like him."

In 2007, Mr Jackson was injured trying to save a toddler from a burning apartment building.

Other victims

Baton Rouge Police Chief Carl Dabadie jnr said a 41-year-old police officer with just under a year on the force died in the attack.

Also among the dead was an East Baron Rouge Parish sheriff's deputy, who was 45, Sheriff Sid Gautreaux said.

US media have identified the other officers killed, besides Mr Jackson, as Matthew Gerald, 41, and Brad Garafola.

Baton Rouge television station WAFB said Mr Gerald graduated from the Baton Rouge Police Department four months ago.

He was a former Marine and Black Hawk crew chief in the US Army, WAFB said.

Mr Gerald was married with two children, WAFB said.

Mr Garafola was an East Baton Rouge Parish Sheriff's deputy, television station WBRZ reported.

His brother, Brett, posted a message on Facebook late on Sunday, saying Mr Garafola "leaves his wife and 4 kids behind in which he loved so much".

"Brad, I love you very much my brother. I respect and appreciate everything you did for us, this city, and your job to protect and serve," he wrote.

Mr Gautreaux said a 41-year-old sheriff's deputy was in critical condition, "fighting for his life as we speak".

In addition, one sheriff's deputy was in surgery for non-life-threatening injuries, he said.

A 41-year-old Baton Rouge police officer, on the force for nine years, also received a non-life-threatening injury, Mr Dabadie said.

with Reuters, AP