On the last day of 2011, US President Barack Obama Saturday signed into law measures penalizing foreign financial institutions doing business with Iran's central bank, Bank Markazi - the toughest sanctions imposed yet over Iran's development of a nuclear weapon. In recent weeks Tehran has repeatedly warned that it would deem the signing of this measure an act of war and respond with drastic steps including the closure of the Strait of Hormuz.
The bill targeting anyone dealing with Iran's central bank seeks to force other countries to choose between buying oil from Iran or being shut out of transactions with US financial institutions and banks.  The new sanctions will begin taking effect in 60 days – the toughest not for at least six months, giving Tehran some space to cooperate with international demands to call off its nuclear weapon program. The president will have some flexibility in applying the measure.