Protests have spread to cities across the US against a decision not to charge a white police officer who shot dead an unarmed black teenager.
Thousands of national guard troops are now in Missouri to try to avoid a second night of rioting there, and peaceful protests have been held in other major cities.
The family of Michael Brown - who was shot dead - says the decision not to bring charges is unfair, and they criticised the Grand Jury process.
President Obama says he has no sympathy for people who use what happened as an excuse for violence.
But he says he will work to make sure law enforcement in the US is fair:
