US presidential candidate Jeb Bush has said the United States should focus assistance on Christian refugees fleeing persecution.

"We should focus our efforts as it relates to refugees on the Christians that are being slaughtered," he told CNN's 'State of the Union' on Sunday morning.

Unlike other Republican candidates, Bush has not called for an outright ban on accepting refugees from the Middle East, however he has said that we should prioritise Christians.

While he conceded that determining whether a refugee is Christian through screening would be a "national security challenge", he maintained that "we do that a lot" already as the country screens potential refugees for relocation.

The terrorist attacks in Paris are "a warning for our country that the threat is not going to go away," he said.

"This is a threat against Western civilization, and we need to lead. The United States has pulled back, and when we pull back, voids are filled and they're filled right now by Islamic terrorism that threatens our country."

He has criticised the Obama administration: "The president has admitted he does not have a strategy as it relates to ISIS. Hillary Clinton last night said that it's not our fight," Bush said.

"It is our fight, and without our leadership to build a coalition to destroy ISIS, it won't happen."