Pakistan's foreign exchange reserves fell to $17.31 billion in the week ending February 5, down from a record $17.38 billion the previous week, the central bank said on Thursday. Reserves held by the State Bank of Pakistan (SBP) fell to $13.76 billion from $13.85 billion in the week ending February 5, while those held by commercial banks rose to $3.55 billion from $3.53 billion, said the SBP.