WASHINGTON (Reuters) -- President Barack Obama signed a sweeping defense policy bill into law on Wednesday, legislation that authorizes $607 billion in defense spending but also includes provisions that make it harder to close the military prison at Guantanamo Bay, Cuba.

The White House had made it clear earlier this month that Obama would sign the bill despite the Guantanamo provisions. Obama has long promised to close the prison, but has faced objections from lawmakers who do not want detainees to be transferred to U.S. prisons.

"As I have said before, the continued operation of this facility weakens our national security by draining resources, damaging our relationships with key allies and partners, and emboldening violent extremists. It is imperative that we take responsible steps to reduce the population at this facility to the greatest extent possible and close the facility," Obama said in a separate White House statement.

He noted that the detainee population at Guantanamo had been reduced by over 85 percent from its peak, including 57 transfers over the past 24 months.

If the ban on detainee transfers violated constitutional separation of powers principles, Obama said, his administration would "implement them in a manner that avoids the constitutional conflict."

He also expressed disappointment that Congress had "failed to enact meaningful reforms to divest unneeded force structure, reduce wasteful overhead, and modernize military healthcare."

(Reporting by Roberta Rampton and Eric Walsh; editing by Mohammad Zargham andDavid Gregorio)