BATON ROUGE, La. — A former Marine dressed in black and carrying extra ammunition ambushed police in Baton Rouge, shooting and killing three law enforcement officers less than two weeks after a black man was fatally shot by police there in a confrontation that sparked nightly protests that reverberated nationwide.

Three other officers were wounded Sunday, one critically. Police said the gunman was killed at the scene.

“His movements, his direction, his attention was on police officers,” state police Col. Mike Edmonson said Monday morning. He would not elaborate but said the gunman “certainly was seeking out police officers,” and he used the word “ambush” to describe the attack.

Edmonson also confirmed that investigators have interviewed people with whom the shooter had contact in Baton Rouge. But Edmonson wouldn’t say how many or give details. He stressed that the interviews don’t mean that those people were involved in the shooting and urged any others who might have had contact with or information about shooter Gavin Long to come forward.

The shooting less than a mile from police headquarters added to the tensions across the country between the black community and police. Last week, a gunman targeted police during a march in Dallas, killing five officers. And just days before the Baton Rouge attack, one of the slain officers had posted an emotional Facebook message about the challenges of police work in the current environment.

President Barack Obama urged Americans to tamp down inflammatory words and actions.

“We don’t need careless accusations thrown around to score political points or to advance an agenda. We need to temper our words and open our hearts … all of us,” Obama said.

The gunman was identified as Gavin Long of Kansas City, who turned 29 Sunday.

Long, who was black, served in the Marines from 2005 to 2010, reaching the rank of sergeant. He deployed to Iraq from June 2008 to January 2009, according to military records.

Although he was believed to be the only person who fired at officers, authorities were investigating whether he had some kind of help.

“We are not ready to say he acted alone,” state police spokesman Major Doug Cain said. Two “persons of interest” were detained for questioning in the nearby town of Addis. They were later released without any charges being filed.

While in the military, Long was awarded several medals, including one for good conduct, and received an honorable discharge. His occupational expertise was listed as “data network specialist.”

The University of Alabama issued a statement saying Long attended classes for one semester in the spring of 2012. A school spokesman said university police had no interactions with him.

In Kansas City, police officers, some with guns drawn, converged on a house listed as Long’s.

It was the fourth high-profile deadly encounter in the United States involving police over the past two weeks. In all, the violence has cost the lives of eight officers, including those in Baton Rouge, and two civilians and sparked a national debate over race and policing.