United States President Barack Obama is planning to increase the number of refugees admitted to his nation, and is calling on countries like Australia to follow suit.

That is despite fears that terrorists will use refugee flows to infiltrate Western nations.

"Of the approximately 800,000 refugees who have been admitted to the United States since 9/11, not one has carried out an act of domestic terrorism," US Ambassador to the United Nations (UN) Samantha Power said.

That has not stopped US politicians linking the attacks in Orlando or San Bernardino to immigration — both were US citizens of foreign-born parents and the wife in San Bernardino came from Pakistan.

"What is, in fact, counterproductive, is using inaccurate characterisations of threats to justify shifts in policy ... such as failing to see the difference between a homegrown terrorist and a refugee," she said.

"So, it is not lost on me that were such a prejudiced and indiscriminate policy to have been applied by the US when I was growing up [that] my family and millions of other Irish immigrants would never have been allowed to come to this country," she added, herself a migrant from Ireland at a time of 'the Troubles'.

Mr Obama will hold a special Leader's Summit on Refugees ahead of the UN General Assembly in New York on September 20 at which he will call for greater refugee intakes and resources from the international community — including Australia which the Turnbull Government has said is already accepting the highest number of refugees since the end of World War Two.

Of the around 800,000 refugees admitted to the US since 9/11 none have been involved in domestic terrorism, Ambassador Power says. ( ABC News )

"We say thanks for starters [to Australia], and then, 'Can you do more?', given that the UN appeals on the financial side are a quarter filled of the $28.22 billion appeal — given that the displacement of Syrians hasn't ended," Ambassador Power said.

"And only 30 of the 193 countries of the UN have resettlement relationships with the UNHCR [United Nations High Commissioner for Refugees]."

That call comes at a time when more than half of America's 50 states are opposed to helping Syrian refugees.

"We have voices in my own country and governors — 30 governors — who've said, 'We don't want refugees in our state'," she said.

Asked how much harder would the division of nation make her call to double refugee intake, she said the US was in a "good position".

"We've brought our overall refugee numbers up by 40 per cent over the last two years. I think you'll see those numbers steadily increase," she said.

"We're also the largest humanitarian donor in the world. So, I think we're in a good position, but we also know we'll be in a stronger position the more we do.

"So, we're seeking to win the debate domestically: tip the politics in favour of doing more."

'We regret having heeded voices of fear'

Security and fear are major components in the refugee and immigration issue in the US.

FBI director James Comey, in evidence to the US Congress, said he could not offer an absolute assurance that there was no risk associated with the intake of refugees.

"I mean, the idea of risk elimination in public policy is not one that any of us could ... none of us would be driving on the roads," Ambassador Power said.

"I think that in our history arguments like that have often been very voluble. They've often even swayed the majority of the American people [citing WWII, Korea, Vietnam, Hungary, Iraq].

"We always look back and regret having again heeded the voices of fear."

Watch the full interview on The World tonight at 10:00pm on ABC News24.