The Pentagon is expected to submit a plan to Congress to close the United States military prison at Guantanamo Bay, setting up a battle with politicians who oppose President Barack Obama's efforts to close down the facility.
Obama, whose pledge to shut down the prison on a naval base in Cuba dates back to the start of his presidency, is seeking to make good on his promise before he leaves office next January.
Captain Jeff Davis, a Pentagon spokesman, said that the administration intended to meet Tuesday's deadline to present a detailed proposal for closing the facility. There are still 91 prisoners held there.
"We understand the deadline is tomorrow, and it's our intent to meet it," Davis said on Monday.
US officials have said the plan will include sending 35 detainees who are cleared for transfer to either their home country or to a third country.
The remaining prisoners would be brought back to US soil and held in maximum-security prisons. Congress has banned such transfers to the US mainland since 2011.
Another option will be the possibility of sending some prisoners overseas for prosecution and trial, one US official said, according to the Reuters news agency.
The plan could also serve as a template for how to deal with future combatants captured in the fight against the Islamic State of Iraq and the Levant (ISIL) group.
The document will not name the alternative US prisons under consideration for housing detainees, US officials said.
READ MORE: What to expect from Obama's plan to close Guantanamo
The administration wants to avoid fuelling any political outcry over specific sites during a US presidential election year.
However, Pentagon officials have already surveyed a federal prison in Florence, Colorado, a military jail at Fort Leavenworth, Kansas, and the naval brig in Charleston, South Carolina.
An effort will also be made to speed up parole-style reviews to determine whether more prisoners can be added to the group cleared for release, officials said.
The plan will include costs for upgrading US facilities and housing the inmates there, according to a source familiar with the matter. The White House last year rejected one Pentagon proposal as being too expensive, sending it back for revisions.
Republicans and some Democrats in Congress largely oppose proposals to move any of the prisoners to the US mainland.
Republican Senator Kelly Ayotte said on Monday that the Obama administration refused to "level with the American people regarding the terrorist activities and affiliations of the detainees who remain at Guantanamo".
White House spokesman, Josh Earnest, reiterated Obama's view of Guantanamo as a "recruiting tool" for enemies of the US and urged politicians to look at the plan "with an open mind", although he expressed doubt about whether they would do so.
The White House has left open the possibility that Obama might resort to executive powers to close the facility.
The prison was opened in 2002 by former President George W Bush to house foreign suspects rounded up after the September 11, 2001, attacks in New York and Washington.
The US quickly drew criticism from human rights activists and foreign governments over Guantanamo, where most prisoners have been held for more than a decade without trial.