ISLAMABAD, April 27 -- Pakistan's political and military leadership was scrambling on Sunday to reignite ceasefire talks between the United States and Iran after President Donald Trump told envoys not to travel to Islamabad for negotiations this weekend, Pakistani officials said. Two Pakistani officials, speaking on condition of anonymity to discuss the efforts, did not say when the Americans might return to the region. Iran wants to persuade Oman to support a mechanism to collect tolls from vessels passing through the strait, through which a fifth of the world's oil flows in peacetime, according to a regional official who spoke on condition of anonymity. The official, who is involved in mediation efforts, said Iran insists on ending the US...