FERGUSON, Mo — Police here fired tear gas, stun grenades and smoke bombs to disperse several hundred protesters late Wednesday, the fourth night of racially charged demonstrations after police shot and killed an unarmed Black teenager.

Protesters have gathered every night since Saturday when 18-year-old Michael Brown was killed by police in the mostly Black suburb of St. Louis. Witnesses said Brown had his hands raised in the air at the time of the shooting, while police said there was a struggle over a gun in the police car.

“I’ve had enough of being pushed around because of the color of my skin. I’m sick of this police brutality,” one protester, who only gave his first name, Terrell, said. “I’m going to keep coming back here night after night until we get justice.”

At least 10 protesters were arrested overnight, the St. Louis Post-Dispatch reported. At least 50 have been arrested since Saturday. 

Ferguson Police Chief Thomas Jackson, who has been the public face of the city torn by Brown’s death, told reporters earlier in the day that the St. Louis County investigation of the shooting could take weeks to complete.

In the meantime, he said, his department welcomes Justice Department training on race relations in the suburb, where two-thirds of the 21,000 residents are Black while all but three of the police force’s 53 officers are white.

Residents in the low-income, mostly Black neighborhood where Brown was killed say they are often harassed by police. Ferguson has seen a sharp demographic shift in recent decades, going from virtually all White to mostly Black. 

“Unfortunately, an undertow [of racial unrest] has bubbled to the surface,” said Jackson. “Race relations is the top priority right now.”

While Jackson said he wanted to mend fences with the community, protesters were on the streets of Ferguson again on Wednesday, facing heavily armed police who at one time fired weapons at them from an armored truck.

Multiple journalists reporting at the scene have reportedly faced pressure from Ferguson police. On Wednesday evening, reporters Wesley Lowery of The Washington Post and Ryan J. Reilly of The Huffington Post wrote on Twitter that they had been assaulted and detained by police, who at the time were attempting to “kick everyone out” of McDonald’s.

“Detained, booked, given answers to no questions. Then just let out,” Lowery tweeted. 

The Washington Post reported that Lowery said he was slammed against a soda machine and plastic cuffs were put on his wrists. Reilly told MSNBC that an officer slammed his head against the glass “purposefully” on the way out of the restaurant “and then sarcastically apologized for it.” The reporters were subsequently released without any charges.

Martin D. Baron, The Washington Post’s executive editor, issued a statement saying “there was absolutely no justification” for Lowery’s arrest and said the organization was appalled by the officers’ conduct.

President Obama spoke about the situation in Ferguson on Thursday. He said there are “no excuses” for excessive police force there.

“I know that emotions are raw right now in Ferguson,” Obama said at a news conference this afternoon. “There is never excuse for violence against the police or for those who would use this tragedy as a cover for vandalism or looting. … There is also no excuse for police to use excessive force against peaceful protests or to throw protesters in jail. Police should not be bullying or arresting journalists who are just trying to do their jobs.”

Obama’s comments came as the FBI told ABC News that it issued a warning to police officers that a Black Panther leader was trying to incite violence against law enforcement in Ferguson, a suburb of St. Louis.

Obama first addressed the issue on Tuesday when he released a statement saying that Department of Justice was investigating Brown’s death alongside local officials.

“I know the events of the past few days have prompted strong passions, but as details unfold, I urge everyone in Ferguson, Missouri, and across the country, to remember this young man through reflection and understanding,” President Obama said Tuesday as he took time off from a vacation in Martha’s Vineyard.

“We should comfort each other and talk with one another in a way that heals, not in a way that wounds. Along with our prayers, that’s what Michael and his family, and our broader American community, deserve.”