"I don't know," Mr Holder told a House of Representatives appropriations subcommittee. "We will do all that we can."
Mr Holder declined to offer any new details about plans on how the administration will prosecute terrorism suspects held at the Guantánamo Bay prison, but he said repeatedly that the administration still planned to close the facility.
The U.S. Congress has barred the Obama administration from bringing any detainees to U.S. soil for prosecution or detention, significantly hampering the effort to close the prison.
Obama administration officials have said the prison serves as a recruiting tool for anti-American militants and has made it hard to negotiate with some U.S. allies to take in detainees who have been cleared of any wrongdoing.
Republicans and even some of Obama's fellow Democrats have opposed bringing terrorism suspects to U.S. soil for prosecution in traditional federal courts and instead want them tried in special military commissions at the Guantánamo prison.