More than 1600 refugees have expressed interest in a resettlement deal with the United States, which is expected to offer up to 1250 places.
The detainees on Manus Island and Nauru are slated to resettle in America under the one-off deal struck by the Australian government, with US officials vetting refugees to decide who will be accepted.
As of March 22, some 1626 refugees and transferees had expressed interest in being considered for resettlement. The vast majority (1253) were men, with 228 women and 145 minors.
Immigration officials say the most vulnerable refugees will be given priority, with an initial focus on women, children and families.
"The US considers refugees as cases. A case may comprise of a family group, either nuclear or extended, or as an individual," the department said in response to questions posed in Senate estimates.
Immigration officials did not specify either minimum or maximum numbers of refugees the US has agreed to take under the deal, pointing instead to an "indicative planning" number of 1250.
Asked about continency plans for anyone not accepted under the deal, the department said refugees on Nauru had the option of staying there for up to 20 years or volunteering for resettlement in Cambodia.
Refugees on Manus Island could settle in Papua New Guinea, while anyone found not to be in need of international protection would be expected to return home and given assistance to do so.
Since the signing of the US deal, Australia has pumped an extra $7 million into on-water and air surveillance as well as an additional $15 million for a range of other costs.
Department officials said there was no financial element to the resettlement deal and Australia was not asked to provide support to refugees settled in the US.
They would not say when the deal was signed or by whom, nor when it went to cabinet.
However, they confirmed Australia had not agreed to accept a specific number of people from Costa Rica refugee camps.
Asked if any other countries had approached Australia regarding remaining refugees following announcement of the US deal, the department said Australia has had discussions with other countries to expand options for the resettlement of refugees on Manus Island and Nauru.
"It is not appropriate to disclose details of confidential discussions with other governments," the department said.
