EDGARTOWN, Mass. » Appealing for "peace and calm," President Barack Obama on Thursday said there is no excuse for excessive use of force by police in a St. Louis suburb against crowds protesting the death of an unarmed black teenager shot by a white police officer. At the same time, he said there was no excuse for violence against police.

Obama appeared to try to balance his comments as he addressed the turbulent aftermath of the shooting of 18-year-old Michael Brown, who was killed Saturday.  

Obama said there was "no excuse for police to use excessive force against peaceful protests or to throw protesters in jail for lawfully exercising their First Amendment rights" and also criticized police for arresting two journalists covering the racially charged clashes. 

"Put simply, we all need to hold ourselves to a high standard, particularly those of us in positions of authority," Obama said in his first in-person remarks on the situation in Ferguson, Missouri. He spoke from Martha’s Vineyard, the Massachusetts island where he is in the midst of a two-week vacation. 

Obama said he had asked the Justice Department and FBI to investigate Brown’s death. The president said he had also spoken Thursday morning with Missouri Gov. Jay Nixon, who has faced criticism for not doing more to control the violence.

Obama defended the Democratic governor, calling him "a good man, a fine governor." 

Police in Ferguson have stood by their use of tear gas and smoke bombs to repel protesters, saying they took those actions to disperse a large crowd after some people threw Molotov cocktails and rocks at officers. Obama also urged the protesters to show restraint, saying there is "never an excuse for violence against police or for those who would use this tragedy as a cover for vandalism or looting."

There are varying accounts about what led to Brown’s death. 

Police say that after encountering Brown and another man on the street, one of the men assaulted an officer and struggled with him over his weapon. During the struggled, Brown was shot multiple times. 

But a man who says he was with Brown during the shooting has told a much different account. Dorian Johnson says the officer grabbed his friend’s neck, then tried to pull him into the car before brandishing his weapon and firing. Johnson and another witness both say Brown was on the street with his hands raised when the officer fired at him repeatedly. 

"I know emotions are raw right now in Ferguson and there are certainly passionate differences about what has happened," Obama said. "But let’s remember that we’re all part of one American family, we are united in common values and that includes the belief in equality under the law, respect for public order and the right to peaceful public protests."