Three US police officers shot dead in Baton Rouge

 Louisiana Officials Give Details on Shooting That Killed Three Police Officers in Baton Rouge (Jonathan Bachman/Reuters)

Three police officers have been killed and three injured in a shooting in the southern US city of Baton Rouge.

A suspect shot dead at the scene was thought to be the only gunman involved, police said. Reports earlier suggested there was more than one gunman.

There was no "active shooting scenario" in the city now, Louisiana Police Superintendent Mike Edmonson said.

The incident follows the recent killing of a black man by police in Baton Rouge, which sparked protests.

Police officers block off a road near the site of a shooting of police in Baton Baton Rouge shooting. (Image: Joe Penney/Reuters)

President Barack Obama said in a statement: "I condemn, in the strongest sense of the word, the attack on law enforcement in Baton Rouge."

He said there was no justification for violence against law enforcement and such attacks "are the work of cowards who speak for no one".

US Attorney General Loretta Lynch said the FBI and other federal agents are at the scene in Baton Rouge and would help with investigations "to the fullest extent possible", Reuters reported.

Louisiana Governor John Bel Edwards told a news conference it was an "absolutely unspeakable, heinous attack."

Mobile phone footage from Baton Rouge showed police cars arriving at a road intersection. Several shots were then heard.

Officers were responding to a report of a man carrying a rifle along a major motorway, Colonel Edmonson told a news conference. He said the gunman was dressed all in black.

Witnesses reported a man firing indiscriminately.

"We believe that the person who shot and killed our officers, that he was the person that was shot and killed at the scene," Col Edmonson said.

US media outlets are naming the gunman as Gavin Long, 29, of Kansas City, Missouri.

Two of the dead were Baton Rouge police officers and one was an East Baton Rouge Parish Sheriff's Office deputy. All three were married and had family.

One of the injured was in a critical condition, while the other two were in a stable condition.

The local sheriff's department spokeswoman told WAFB TV the incident began shortly before 09:00 local time (14:00 GMT).

A witness interviewed by the station said the shooting appeared to have broken out before law enforcement officers arrived at the scene.

Police officers block off a road after a shooting of police in Baton Rouge, Louisiana (Image: Joe Penney/Reuters)

Witness Brady Vancel told WAFB he saw what may have been gang members shooting at each other before police arrived.

Another witness said she saw a gunman wearing a black mask and military-style clothing.

Baton Rouge Mayor Kip Holden said he had spoken to White House officials who had offered assistance. He said it was "a defining moment" for community relations.

But he also told local media the "rhetoric from some people" after the death of Alton Sterling in Baton Rouge may be connected to the shootings, without elaborating who.

"Everything's been anti-police," he said.