FERGUSON, Mo. -- The family of the unarmed black 18-year-old who was fatally shot in Missouri called for calm Friday as a grand jury drew closer to an announcement on whether to charge the officer who shot him.

The St. Louis area was on edge as it awaited word on whether the panel would indict officer Darren Wilson in the Aug. 9 death of Michael Brown.

The shooting of a young black man by a white police officer led to protests, some of which turned violent. The case reigniting a fiery debate in the United States over race relations between police departments and the minority communities they serve. In Ferguson, the city outside St. Louis where Brown was killed, two-thirds of residents are black but the police force is almost entirely white

The FBI has sent nearly 100 additional agents to Ferguson to help law enforcement prepare for possible unrest ahead of the grand jury decision, according to a U.S. official who was not authorized to discuss the FBI plans by name and spoke on condition of anonymity.

Ed Magee, a spokesman for county Prosecutor Bob McCulloch, said Friday in an email to reporters that the grand jury is still reviewing the case. The time, date and place for a news conference announcing the decision had not been decided, he wrote.

Wilson, 28, reportedly told the grand jury he feared for his life as Brown, who was 6-foot-4 and (1.9 metres) nearly 300 pounds (136 kilograms), came at him. Witnesses said Brown was trying to surrender and had his hands up.

Protesters were arrested Thursday outside Ferguson police headquarters for the second night in a row after around 40 demonstrators blocked a road.

President Barack Obama called on protesters to remain peaceful, saying everyone has the right to express their views and assemble peacefully but that the event weas not an excuse for violence.

Calls for peace and restraint emanated from other quarters, as well -- business owners, civil rights leaders and outgoing Attorney General Eric Holder. Most prominently, those calls came from Brown's father.

"Hurting others or destroying property is not the answer," Brown said in the video released by the group STL Forward. "No matter what the grand jury decides, I don't want my son's death to be in vain. I want it to lead to incredible change, positive change, change that makes the St. Louis region better for everyone."

- Salter reported from St. Louis. Associated Press writers Eric Tucker and Jim Drinkard in Washington contributed to this report.