Opponents of Keystone XL pipeline ride horses from Capitol to National Mall

Protesters gathered on the National Mall in Washington DC on Tuesday to demonstrate against the controversial Keystone XL pipeline project. The protest, which is scheduled to last for six days, has been organized by the Cowboy and Indian Alliance, a group of ranchers, farmers and indigenous leaders who want US President Barack Obama to reject the pipeline. A ceremonial horseback ride from the Capitol down the National Mall formed part of Tuesday's protest.

The Keystone XL pipeline project would carry oil from western Canada's tar sands to refineries on the Texas Gulf Coast.