(Updates with Obama quotes, background)
By Jeff Mason and Daniel Lovering
EDGARTOWN, Mass., Aug 14 (Reuters) - U.S. President Barack Obama on Thursday called for peace on the streets of Ferguson, Missouri, after the fatal shooting of an unarmed black teenager by a police officer and urged authorities to be transparent in their investigation.
"Now is the time for healing. Now is the time for peace and calm on the streets of Ferguson," Obama told reporters on Martha's Vineyard, where he is vacationing with his family. "Now is the time for an open and transparent process to see that justice is done."
Protesters have gathered every night in Ferguson, the mostly black suburb of St. Louis, since Michael Brown was fatally shot on Saturday during what authorities said was a struggle over a gun in a police car. Some witnesses say he was outside the car with his hands up.
Obama said he had asked the Department of Justice and the FBI to investigate the killing independently.
He said he expressed concern to Missouri Governor Jay Nixon about violence in the wake of the shooting and noted he had asked Attorney General Eric Holder and the U.S. attorney on the scene to report back to him in the coming days about the investigation.
"We lost a young man, Michael Brown, in heart-breaking and tragic circumstances. He was 18 years old and his family will never hold Michael in their arms again," Obama said.
"When something like this happens, the local authorities, including the police, have a responsibility to be open and transparent about how they are investigating that death and how they are protecting the people in their communities."
Obama said there was never an excuse for looting or violence against police. But he also made a point of saying there was no excuse for police to use excessive force against peaceful protesters or to throw people, including journalists, in jail for exercising their rights under the U.S. Constitution.
"We all need to hold ourselves to a high standard," Obama said.
The Missouri incident recalls Obama's emotional reaction to the shooting of Trayvon Martin, the black teenager who was shot to death by a white Hispanic neighborhood watch volunteer in Florida in 2012.
Obama, the first black U.S. president, compared Martin to a son he did not have and urged "soul searching" over how the incident occurred.
The president has faced criticism since arriving on Martha's Vineyard for spending time golfing or partying with friends while U.S. forces were active in Iraq and mayhem erupted in Ferguson.
The White House rejects that criticism and has said Obama continues to do his job while having some down time to relax. Shortly after completing his statement on the situations in Ferguson and Iraq, Obama went golfing with friends. (Additional reporting by Mark Felsenthal in Washington; Editing by Bill Trott)