Washington, September 2 (RHC)-- U.S. Defense Secretary Ashton Carter has said about half the detainees at the US military prison at Guantanamo Bay, Cuba need to be imprisoned "indefinitely" and cannot be released to other nations.

"Some of the people who are there at Guantanamo Bay have to be detained indefinitely, they've just got to be locked up," Carter told troops on Tuesday during a televised interview. The Pentagon chief said he supports U.S. President Barack Obama's long-standing goal of closing the prison, but warned that about half of Guantanamo detainees are too dangerous to release to other countries.

"There are some, maybe half or so of the population of Guantanamo Bay, that under conditions that are safe ... we may be able to transfer them to some other country," Carter said. "But there's another roughly half of them that are not safe to release, period."

Currently, 116 inmates remain at the prison, which was opened by former President George W. Bush after the September 11, 2001 attacks to house suspected terrorists. The notorious facility has drawn international condemnation for its treatment of prisoners and which human rights organizations say serves as a recruitment and propaganda tool for extremists.

White House spokesman Josh Earnest said on Monday that the Obama administration is considering a "wide array" of options for closing the prison. Earnest said the best path for closing the prison would be gaining congressional approval to do so.

A unilateral move by Obama to close the prison would certainly ignite a political firestorm in Congress. The closure of the jail was among the main election promises of Obama during the 2008 presidential election. Obama vowed to close it within a year when he came to office in 2009. But he quickly became entangled in a political and legal wrangling over what to do with the inmates.