FERGUSON, United States: Tensions rose Saturday in the troubled St. Louis suburb of Ferguson, with a grand jury poised to decide whether to prosecute a white police officer for killing an unarmed black teenager.

US President Barack Obama has called for calm, Missouri’s governor declared a state of emergency and activated the state National Guard, and the FBI has deployed an extra 100 personnel in the city.

Police helicopters trained search lights over Ferguson late Friday as a small gaggle of protesters braved the cold to demand that officer Darren Wilson stand trial for shooting 18-year-old Michael Brown on Aug. 9.

Brown’s killing led to weeks of violence that inflamed racial tensions in the St. Louis suburb of 21,000, which has an African American majority and an overwhelmingly white police force and town government.

“I’m here for justice. If we don’t get justice, aint nobody gonna get no peace,” said 22-year-old Ebony, who works in security and refused to give a second name.

“We’re going to keep protesting until we know what’s right gets done,” she told AFP late Friday. “I want to see Darren Wilson go to jail.” Brown, a high-school graduate planning on attending technical college, was shot at least six times by Wilson. His body was left in the street for hours.

Wilson reportedly told the grand jury he acted in self-defense after tussling with the youth. Others claim Brown had his hands up in the air when he was shot.