US President Barack Obama Saturday signed a huge defence bill into law despite his \"serious reservations\" that it seeks to force his hand on Guantanamo Bay and military trials for terror suspects. Obama, on vacation in Hawaii, added a signing statement to the $662 billion law, laying out objections to its constraints on detaining and prosecuting suspects, and directing government agencies on how to interpret them. \"I have signed this bill despite having serious reservations with certain provisions that regulate the detention, interrogation, and prosecution of suspected terrorists,\" Obama said in the statement. He argued that recent US successes against Al Qaeda had been possible because counterterrorism authorities had benefited from flexibility on dealing with suspects, which the bill called into question. \"Against that record of success, some in Congress continue to insist upon restricting the options available to our counterterrorism professionals and interfering with the very operations that have kept us safe,\" Obama wrote. \"The fact that I support this bill as a whole does not mean I agree with everything in it,\" Obama said in a statement, citing limits on transferring detainees from the US base at Guantanamo Bay, Cuba, and requirements he notify Congress before sharing some defence missile information with Russia as problematic. Iran sanctions The US defense funding bill Obama signed on Saturday includes new sanctions on financial institutions dealing with Iran\'s central bank. The bill, approved by Congress last week, aims with its Iran sanctions to reduce Tehran\'s oil revenues but gives the US president powers to waive penalties as required. Senior U.S. officials said Washington was engaging with its foreign partners to ensure the sanctions can work without harming global energy markets, and stressed the U.S. strategy for engaging with Iran was unchanged by the bill.