Oregon standoff: Why US police are surrounding a nature reserve

US law enforcement agents have surrounded a wildlife refuge in the western state of Oregon which has been occupied by an armed militia since early January.

One man was killed and eight people - including militia leader Ammon Bundy - were arrested during a traffic stop on Tuesday.

The militia says it is supporting two ranchers jailed for setting fire to federal land, and accuses the US federal government of taking land illegally from ranchers.

BBC News examines the story behind the protest.