KARACHI, Pakistan, Dec 27 (Reuters) - Pakistan's foreign exchange reserves decrease $591 million to $7,457.3 million in the week ending Dec 21, compared to $8,048.3 million in the previous week, central bank said on Thursday. RESERVES Week ending Previous Week Change/pct ($ billions) Dec 21 Held by the State $7,457.3 mln $8,048.3 mln -7.3 Bank of Pakistan Held by $6,560.5 mln $6,536.2 mln 0.3 commercial banks Total $14,017.8 mln $14,584.5 mln -3.8 The reserves decreased $591 million week ending December 21, due to external debt servicing and other official payments, the central bank said on Thursday. (Reporting by Syed Raza Hassan)