The mayor of Dallas, United States, Mike Rawlings on Friday said the city is safe, hours after five law enforcement officers were killed during a protest rally decrying police brutality against African Americans. Officials said a ‘lone shooter’ was involved, 25-year-old Micah Johnson, an army veteran who had served in Afghanistan. Johnson was killed in a standoff with police after long negotiations. He had claimed he wanted to “kill white people, especially police officers” as he was troubled by recent incidents of the police shooting dead innocent African Americans.

The protest rally had been held to mourn the deaths of two black men being fatally shot by police officers in the past week – Philando Castile in Minnesota and Alton Sterling in Louisiana.

The police found a variety of arms and ammunition, including bomb-making material, at Johnson’s home. They eventually killed him by sending in a robot with a bomb and detonating it, officials said.

The incident has worsened the tense race relations in the country, and is being dubbed the deadliest attack on law enforcement authorities in the US since the September 11 violence. Protests intensified all over the country after the shootings, with demands for justice of Castile and Sterling growing alongside further incidents of retaliatory violence against white people. In Tenessee, a woman was killed by black army veteran, while thousands marched for Castile and Sterling in Atlanta. President Barack Obama, who had called the shootings “despicable”, has cut short a trip to Europe. He will visit Dallas next week.