The US State Department has defended its role in the Nauru and Manus Island refugee resettlement deal with Australian Prime Minister Malcolm Turnbull and described its security vetting procedures as "thorough".
It has also outlined how it will attempt to facilitate the deal without taking it through the minefield of the US congress.
US Senate Judiciary Committee chairman Charles Grassley and House of Representatives Judiciary Committee chairman Bob Goodlatte have publicly questioned in recent weeks the State Department and Department of Homeland Security's decision to keep the deal classified and not consult with congress.
The State Department hit back, outlining its stance in a letter, obtained by AAP, to Mr Grassley.
"Our arrangement to accept these refugee referrals does not require a legally-binding international agreement or any changes to the size or scope of the USRAP (US Refugee Admissions Program); in fact, these numbers will be charged to the region of their country of origin discussed in our consultations with Congress and issued in the Presidential Determination," State Department assistant secretary of legislative affairs Julia Frifield wrote.
The two Republicans said media reports first alerted them to the US-Australia deal involving more than 2400 refugees, including some from "countries of national security concern" Syria, Iraq, Somalia, Pakistan and Afghanistan.
"Regarding your concern about considering refugee referrals from the countries highlighted in your letter, these nationalities are not new to the USRAP," Ms Frifield responded.
"The United States already considers UNHCR (United Nations High Commissioner for Refugees) referrals and resettles refugees from all of the countries noted in your letter both in East Asia and worldwide.
"The USRAP continues to implement thorough security vetting procedures for refugees of all nationalities, and the United States will not accept any refugees for resettlement, under this arrangement or otherwise, unless they pass all required security vetting."
The US resettlement of the Australian rejected refugees is at odds with repeated comments by US president-elect Donald Trump who has vowed to block refugees from the Middle East and other global hotspots.
