US says refugee numbers not final

The United States doesn't have a figure on how many refugees it will take from Nauru and Manus Island amid speculation it could limit its intake under a resettlement deal with Canberra.

Immigration Minister Peter Dutton has refused to confirm exact numbers, but is adamant reports the US will only accept between 300 and 400 individuals from family groups are false.

The US embassy in Canberra says the process is still ongoing.

"The United States will determine the number of refugees to be included in the program in consultation with the UN High Commissioner for Refugees and the government of Australia," a spokeswoman told AAP.

"We have not yet finalised that number."

US officials from the Department of Homeland Security will assess and conduct extra checks on refugees on Sunday and Monday.

Labor is concerned about the lack of details.

"We certainly hope for the people who are on Manus Island and Nauru that a third party resettlement option is available to all of them because they have been waiting much too long," deputy leader Tanya Plibersek told reporters in Canberra.

Mr Dutton has flagged concerns confirming exact numbers may lead to fresh boat arrivals, but says he doesn't want people to "conjure up in their minds" the deal is limited by the reported numbers.

Those people who refused to accept the refugee deal would only have a 20-year visa on Nauru and would have their government assistance cut off.

"If you don't accept the United States of America as an outcome then frankly you're not genuine," he said.