The family of Michael Brown, a black 18-year-old killed in Ferguson last summer by a white police officer, will file a wrongful death lawsuit against the city, attorneys for the family said on Wednesday.

Brown's shooting by officer Darren Wilson last August sparked a wave of angry demonstrations and unrest over police violence, particularly against minorities.

The lawsuit will be filed on Thursday morning, lawyers Benjamin Crump and Daryl Parks said in a brief statement.

"Legal counsel will speak with members of the media immediately following" the filing, the lawyers said, but gave no further details, including the amount of damages to be sought.

The filing has been expected since the family said last month it would file the civil case.

That announcement came a day after the US Justice Department cleared Wilson of any civil rights violations in the shooting of Brown last August. But the department's report found racial bias and a pattern of illegal actions against African-Americans by the Ferguson Police Department.

Ferguson police chief Thomas Jackson resigned last month, within days of the report's release.

A grand jury in Missouri decided in November not to bring criminal charges against Wilson, who has since left the police department.