The shooter was identified as Gavin Eugene Long, 29, of Kansas City, Mo. He was killed at the scene. A motive has not yet been determined.
During a press conference, authorities said Long was the sole shooter. One of the three wounded officers is critical with serious wounds.
The officers who were killed were identified as Montrell Jackson, who had a 4-month-old child, Matthew Gerald and Brad Garafola.
At 9 a.m., the officers were responding to a 911 call reporting a person walking around with a gun near Airline Highway and old Hammond Highway. Long was wearing all black and holding a rifle when police arrived on the scene. The shooting involved members of the Baton Rouge Police Department and East Baton Rouge Sheriff's deputies. Police used a specialized robot to check for explosives near the body of the suspect, but there was no indication that explosives were present.
Police-community relations in Baton Rouge have been especially tense since the killing of 37-year-old Alton Sterling, a black man killed by white officers earlier this month after a scuffle at a convenience store. The killing was captured on cellphone video and circulated widely on the internet. In a report obtained by ABC News, the FBI's New Orleans field office warned law enforcement about threats to officers in wake of the shooting of Alton Sterling.
The mother of Sterling's son said she is heartbroken for the officers and their families, and called for peace. In a statement, Quinyetta McMillon said she is disgusted by the despicable act of violence that resulted in the officers' deaths and that all she and her son Cameron want is peace.
President Barack Obama said Sunday that such attacks are happening far too often, and called on Americans to avoid divisive rhetoric.
Louisiana authorities plan to hold a press conference at 2 p.m. Monday.
DETAILS ABOUT GAVIN LONG
Long is a former Marine sergeant who served in Iraq and had no known ties to any extremist groups.
According to military records, Long was a Marine from 2005 to 2010 and rose to the rank of sergeant. He served in Iraq from June 2008 to January 2009, and records show he received several medals during his military career, including one for good conduct. Long, who received an honorable discharge, was listed as a "data network specialist" in the Marines.
University of Alabama spokesman Chris Bryant said Sunday evening that Long was a student for one semester in the spring of 2012.
Bryant says university police had no interaction with Long during that time.
Sunday was his birthday.
CHICAGO REACTS TO POLICE SHOOTING
Sunday morning, the Chicago police department offered condolences to Baton Rouge police.
Our thoughts & deepest condolences are with @BRPD. CPD is following the situation closely & ask that everyone pray for Baton Rouge community— Chicago Police (@Chicago_Police) July 17, 2016
There is no credible threat to officers in Chicago, however the department is already on high alert after the fatal shooting of police officers in Dallas earlier this month.
Illinois Fraternal Order of Police State Lodge President Chris Southwood said, in part, ""How many police funerals must occur before the American public finally says 'enough is enough?' Those involved in recent protests against the police should look at what happened today in Louisiana and immediately and vehemently condemn these cold-blooded murders. A badge should not be a bulls-eye....I urge everyone to pray for the victims and their families whose lives have been shattered by this unspeakable act of violence."
Rainbow PUSH founder Rev. Jesse Jackson released a statement saying in part, "We do not yet know the twisted motive for gunning down six police officers, killing three of them in Baton Rouge, La., this morning just as the city was headed for church. We do know that violence has absolutely no part to play in our civil rights struggle. Those who engage in violence betray our movement and rob it of the moral high ground. We also know that the lack of mental health services and easy access to guns is a lethal combination. So, once again, we must pray for the families of slain police officers. These attacks on our brothers and sisters in blue must stop....."
Statement from Mayor Emanuel on Baton Rouge pic.twitter.com/Fz4izG4PQJ— ChicagosMayor (@ChicagosMayor) July 17, 2016
President Barack Obama issued a statement condemning the attack and offering support to the Baton Rouge Police Department and the East Baton Rouge Sheriff's Office:
"I condemn, in the strongest sense of the word, the attack on law enforcement in Baton Rouge. For the second time in two weeks, police officers who put their lives on the line for ours every day were doing their job when they were killed in a cowardly and reprehensible assault," Obama said. "These are attacks on public servants, on the rule of law, and on civilized society, and they have to stop.
I've offered my full support, and the full support of the federal government, to Governor Edwards, Mayor Holden, the Sheriff's Office, and the Baton Rouge Police Department. And make no mistake - justice will be done.
We may not yet know the motives for this attack, but I want to be clear: there is no justification for violence against law enforcement. None. These attacks are the work of cowards who speak for no one. They right no wrongs. They advance no causes. The officers in Baton Rouge; the officers in Dallas - they were our fellow Americans, part of our community, part of our country, with people who loved and needed them, and who need us now - all of us - to be at our best.
Today, on the Lord's day, all of us stand united in prayer with the people of Baton Rouge, with the police officers who've been wounded, and with the grieving families of the fallen. May God bless them all."
Hillary Clinton condemned the attack on law enforcement in Baton Rouge.
In a statement on Sunday afternoon the Democratic presidential nominee said, "There is no justification for violence, for hate, for attacks on men and women who put their lives on the line every day in service of our families and communities."
Clinton said that violence must be rejected to "strengthen our communities."
Republican presidential candidate Donald Trump took to Facebook and Twitter and wrote, "We grieve for the officers killed in Baton Rouge today. How many law enforcement and people have to die because of a lack of leadership in our country? We demand law and order" and "We are TRYING to fight ISIS, and now our own people are killing our police. Our country is divided and out of control. The world is watching."
We are TRYING to fight ISIS, and now our own people are killing our police. Our country is divided and out of control. The world is watching— Donald J. Trump (@realDonaldTrump) July 17, 2016