Confronting another killing of police officers, President Barack Obama on Sunday urged Americans to tamper down inflammatory actions as a violent summer collides with the nation’s heated presidential campaign.

Obama said the motive behind Sunday’s killing of three officers in Baton Rouge, Louisiana, was still “unknown.” It was the latest of deadly incidents involving law enforcement, including the police shooting of a black man in Baton Rouge and the killing of five officers in Dallas.

“We as a nation have to be loud and clear that nothing justifies attacks on law enforcement,” Obama said in remarks from the White House briefing room. “We don’t need inflammatory rhetoric. 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.”

It wasn’t long before presumptive GOP nominee Donald Trump blasted Obama’s “lack of leadership” in the country.

“We grieve for the officers killed in Baton Rouge today. How many law enforcement and people have to die because of a lack of leadership in our country? We demand law and order,” Trump said.