Ferguson police blame 'small number of violent agitators'
US police say they have arrested 31 people during another night of angry protests in the town of Ferguson in the state of Missouri.
Unrest flared hours after President Obama called for calm following the fatal police shooting of unarmed black teenager Michael Brown on 9 August.
The US attorney general is due to visit Ferguson on Wednesday to meet federal officials investigating the killing.
The National Guard has been deployed to support police operations.
Police Captain Ron Johnson said officers were forced to fire tear gas on Tuesday after they came under heavy gunfire, and were attacked with petrol bombs and bottles.