Militants claim Khawery Mehsud was killed by a U.S. drone in Afghanistan.
Senior party leaders, including chief Altaf Hussain, deny Saulat Mirza’s allegations.
Foreign ministry spokeswoman says Islamabad is engaging with E.U. on the matter.
Charges unlikely to prompt immediate action against MQM chief, who remains in self-exile in London.
Agency director says current facilities are insufficient to adequately prepare agents for service.
Interior minister says perpetrators of mob lynching will be identified through camera footage and placed under arrest.