American minister and civil rights activist Reverend Al Sharpton on Sunday called the shooting death of unarmed black teenager, Michael Brown, a "defining moment" for the United States.

Speaking at a rally in the town of Ferguson, Sharpton said he wants Congress to stop programmes that provide military-style weaponry to police departments.

He also condemned the recent spate of violence and looting in Ferguson.

Protests have been ongoing since Brown's death heightened racial tensions between the predominantly black community and mostly white Ferguson Police Department, leading to several run-ins between police and protesters and prompting Missouri's governor to put the state highway patrol in charge of security.

Meanwhile, Attorney General Eric Holder has ordered a federal medical examiner to perform another autopsy on Brown.

The "extraordinary circumstances" surrounding the death of the 18-year-old, and a request by Brown's family members prompted the order, Department of Justice spokesman Brian Fallon said in a statement.

The Justice Department had already deepened its civil rights investigation into the shooting.

Officials said 40 FBI agents were going door-to-door gathering information in the Ferguson, Missouri, neighbourhood where Brown, who was unarmed, was shot dead on August 9 in the street.

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AP TELEVISION

1. Wide of audience at rally in Ferguson

2. SOUNDBITE (English) Ty Pruitt, Michael Brown's Cousin:

"This (holds up hands), was the last actions that our family member made before he went to rest. This (holds up hands), will be stuck in my family's memories for the rest of our lives. So when you protest, (holds up hands)."

3. Brown's parents on stage

4. SOUNDBITE (English) Benjamin Crump, Family lawyer:

"So when we say what we're here for today, united for justice, for Michael Brown junior. What we're really asking for is simple justice. We're not asking for anything extraordinary, they just want what anybody else will want if their children was shot down in broad daylight. A fair and impartial investigation. They want to know that they will have their day in court, that the killer of their child will be held accountable to the full extent of the law."

5. Reverend Al Sharpton shaking hands with parents on stage

6. SOUNDBITE (English) Reverend Al Sharpton, National Action Network:

"The debate is how the rights of people are dealt with by the state. Ferguson and Michael Brown Junior will be a defining moment on how this country deals with policing and the rights of its citizens to redress how police behave in this country."

7. Cutaway of Michael Brown's family

8. SOUNDBITE (English) Reverend Al Sharpton, National Action Network:

"While this mother and this father and their families haven't even had the time to bury their son, the police chief would release a tape trying to disparage his name while his mama's still weeping, while the family hasn't even laid him to rest. How can the young folk of the city believe in a system that would try to spit on the name and character of a young man who hasn't even been buried."

9. Cutaway of audience

10. SOUNDBITE (English) Reverend Al Sharpton, National Action Network: ++END OF SOUNDBITE OVERLAID WITH SHOT 11++

"We need to go to Congress after they come back from break, we going to call the day, we'll announce it (inaudible), we're going to have a arms up rally and march in DC (Washington DC) to demand federal legislation around policing how we get police and community to work together."

11. Audience giving standing ovation holding hands in air, cheering

12. Cutaway of Reverend Jesse Jackson in audience at rally