U.S. President Barack Obama signed into law on Saturday a defense funding bill that imposes sanctions on financial institutions dealing with Iran's central bank. The sanctions target both private and government-controlled banks - including central banks - and would take hold after a two- to six-month warning period, depending on the transactions, a senior Obama administration official said. Under the law, the president can move to exempt institutions in a country that has significantly reduced its dealings with Iran and in situations where a waiver is in the U.S. national security interest or otherwise necessary for energy market stability. He would need to notify Congress and waivers would be temporary, but could be extended. Sanctioned institutions would be frozen out of U.S. financial markets, according to a report of Reuters.