KARACHI: Total liquid foreign exchange reserves of the country fell $20.436 billion during the week ended July 21 from $20.830 billion a week ago, the central bank said on Thursday. The foreign exchange reserves held by the State Bank of Pakistan (SBP) dropped $476 million to $15.003 billion due to the payments on account of external debt servicing and other official payments. The foreign exchange reserves of commercial banks rose to $5.433 billion as compared to $5.351 billion in the preceding week.