Washington - President Barack Obama condemned as "cowardly" a shooting that killed three police officers and wounded three more in the Louisiana capital of Baton Rouge on Sunday."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 in a statement."These are attacks on public servants, on the rule of law and on civilised society, and they have to stop."A separate shooting in Dallas, Texas earlier this month killed five police officers during a demonstration triggered by the fatal police shooting of two African American men whose dying moments were captured in shocking video footage that went viral online.Obama said he had offered his "full support" and that of the federal government to authorities in Baton Rouge and to Louisiana state as a whole."And make no mistake - justice will be done," the president added."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."Obama stressed that the police officers in Baton Rouge, like those in Dallas before them, "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".The first African American president of the United States, Obama has made repeated calls for racial unity.During a memorial for the slain policemen, he insisted that "we are not as divided as we seem".