Federal and state authorities on Wednesday urged the group, inside the US Malheur National Wildlife Refuge, to leave.

"If the people at the refuge want to leave, they can do so through the checkpoints where they will be identified," said Greg Bretzing, the US Federal Bureau of Investigation's special agent in charge of the Portland office, during a press briefing.

"Let me be clear: It is fully and unequivocally the behavior and the choices made by the armed occupiers that have led us to where we are today," Bretzing added.

Ammon Bundy, who led the occupation, and seven others were arrested on Tuesday. However, a man identified by activists as Robert LaVoy Finicum - considered the group's de facto spokesperson - was killed after authorities attempted to detain him during a traffic stop.

"I'm disappointed that a traffic stop yesterday that was supposed to bring peaceful resolution to this ended badly," said Harney County Sheriff Dave Ward, adding that the protesters should have voiced their grievances through appropriate channels.

The sheriff did not go into further details citing an on-going investigation into the incident.

'Stand by'

Various self-styled militias, including Oath Keepers and Pacific Patriots Network, said in an official statement that they were issuing an immediate "stand by" order to their members and supporters.

"We must reiterate the current standing order. No mobilization of any kind is to take place until every piece of speculation and hearsay have been verified or dismissed," the statement said.

Authorities have not said how many are still left in the refuge.

ls/jr (Reuters, AFP, AP)