A grand jury has reached a decision about whether to charge a white police officer in the shooting dead of Michael Brown, an unarmed black 18-year-old, US prosecutors say.
The panel has been considering charges against Darren Wilson, the suburban St Louis officer who fatally shot Brown after a confrontation in August.
In a brief email to reporters, St Louis County prosecutor spokesman Ed Magee said the decision would be announced later on Monday.
The August 9 killing of Mr Brown reignited a debate over how police treat young black men in the US.
It drew attention to racial tensions simmering in Ferguson and other US communities four decades after the civil rights movement of the 1960s. The tensions have evoked other racially charged cases, including the riots that rocked Los Angeles in 1992 after the acquittal of white police officers in the videotaped beating of black motorist Rodney King.
More recently, peaceful protests followed the 2013 not-guilty verdict in the Florida slaying in unarmed black teenager Trayvon Martin by George Zimmerman, who was not a police officer but co-ordinated the local neighbourhood watch.
Missouri Governor Jay Nixon was travelling to St Louis from the Capitol on Monday, spokesman Scott Holste told the AP, but did not say why.
Speculation about the timing of an announcement swirled and largely peaceful protests took place during the weekend after the grand jury met on Friday but apparently did not reach a decision.
Many had thought a grand jury decision would be announced on Sunday, based partly on a stepped-up police presence in the preceding days.
The 12-person grand jury deliberates in secret and sets its own schedule depending upon when the members are available.
Benjamin Crump, a lawyer for Mr Brown’s family, said on Sunday that they were frustrated the prosecutor did not charge Wilson himself or suggest a charge to grand jurors.