President Barack Obama
President Barack ObamaReuters

US President Barack Obama has labeled the deadly shooting of three police officers and the wounding of three others in Baton Rouge, Louisiana, as "the work of cowards."

Gunmen - at least some of whom were seen wearing military-style fatigues and at least one of whom was brandishing an assault rifle - opened fire on officers responding to reports of an armed man walking along Airline Highway Sunday.

In a written statement to the press, Obama condemned the attack "in the strongest sense of the word", and vowed the perpetrators would be brought to justice.

"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," the president said.

He added that he had offered his "full support" to local authorities, and vowed: "make no mistake - justice will be done."

The latest deadly attack on American police officers follows the murders of five cops in Dallas, Texas ten days earlier. That attack was the work of a black extremist, who told of his desire to kill white people, and occurred against the backdrop of anti-police brutality marches following the deaths of several black suspects at the hands of police.

The shooting in Baton Rouge - which has also seen major rallies following the shooting dead of black resident Alton Sterling - was also initially believed to have been connected to the racially-charged tensions. However, over the past two hours conflicting reports have emerged, some of which suggested the officers were in fact struck during a gun battle between feuding criminal gangs.

None of the reports have been confirmed yet, and police say they are pursuing all leads.

One of the gunmen was shot dead by police, while two others are still at large and the subject of a major police manhunt.

But President Obama insisted that the precise motive was immaterial as far as punishing those responsible is concerned.

"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," he emphasized.

"These attacks are the work of cowards who speak for no one," the president continued.

"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."