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(CNN) —  

President Barack Obama on Sunday condemned violence against law enforcement and called on Americans to “temper our words and open our hearts,” in the wake of the slaying of three Louisiana law enforcement officers.

“We as a nation have to be loud and clear that nothing justifies violence against law enforcement. Attacks on police are an attack on all of us, and the rule of law that makes society possible,” Obama said, speaking from the White House press 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.”

The tensions between police departments and the communities they serve have consumed much of the president’s time over the past week. He traveled to Dallas Tuesday for a memorial service held after five police officers were gunned down. Later he gathered law enforcement professionals at the White House for talks on how to improve relations between officers and citizens.

In remarks following that meeting, Obama warned that the violence wasn’t likely to immediately end. Those words seemed prescient Sunday, when the President arrived in the briefing room for a rare weekend appearance.

“Only we can prove, through words and through deeds, that we will not be divided,” he said. “And we’re going to have to keep on doing it again and again and again. That’s how this country gets united.”

The President said a fourth police officer in Baton Rouge remains in critical condition and that the killer’s motive was still unknown.

In his brief remarks, Obama stressed the importance of staying away from divisive rhetoric and actions, particularly ahead of two weeks of the Republican and Democratic conventions where he predicted that political rhetoric would be “more overheated than usual.”

“Around the clock news cycles and social media sometimes amplify these divisions,” Obama said. “That is why it is so important that everyone: regardless of race or political party or profession, regardless of what organizations you’re a part of, everyone right now focus on words and actions that can unite this country rather than divide it further.”

The President also stressed – as he did after a police ambush in Dallas – the danger that police face day-to-day.

“The death of these three police officers underscore the danger that police across the country confront every single day,” he said.

Unlike after his most recent remarks following U.S. shooting incidents, Obama did not make any calls – overt or otherwise – for tighter gun control laws. Following last week’s Dallas shootings, Obama did lament the ease with which Americans can access high-powered firearms.

And he also didn’t attempt to balance his praise of law enforcement with an insistence they change some of their tactics.

Instead, Obama offered full-throated support for departments and officers, some of whom say they feel under siege.

“I’ve spent a lot of time with law enforcement this past week,” Obama said. “I’m surrounded by the best of the best every single day. And I know whenever this happens, wherever this happens, you feel it. Your families feel it. But what I want you to know today is the respect and the gratitude of the American people for everything that you do for us.”

The shooting deaths of the three law enforcement officers, with three more injured, came in Baton Rouge – a city already on edge after an African-American man recently was shot and killed by police.

Obama’s remarks Sunday afternoon drew scorn form Donald Trump, the presumptive Republican nominee. Within minutes he issued a series of critical tweets.

“President Obama just had a news conference, but he doesn’t have a clue. Our country is a divided crime scene, and it will only get worse!”

“Our country is totally divided and our enemies are watching. We are not looking good, we are not looking smart, we are not looking tough!”

Hillary Clinton, the presumptive Democratic nominee, issued a statement early Sunday evening similar in tone to President Obama.

“Today’s devastating assault on police officers in Baton Rouge is an assault on all of us. There is no justification for violence, for hate, for attacks on men and women who put their lives on the line every day in service of our families and communities,” she said.

“We must not turn our backs on each other. We must not be indifferent to each other. We must all stand together to reject violence and strengthen our communities. Our thoughts and prayers are with the friends and families of the police officers who were killed and injured today.”