WASHINGTON: Barack Obama will attend a Summit of the Americas in Panama this week, a gathering that could see the first substantive meeting between US and Cuban leaders in half a century. The US president, fresh from reaching a tentative nuclear accord with arch-foe Iran, will jet to Jamaica then on to Panama City Thursday for a regular meeting of continental leaders. Raul Castro — who took control of the 11-million-strong still nominally Communist island from his brother Fidel seven years ago—has confirmed he will be the first Cuban leader to attend. But with days to go, diplomats are still discussing what form a Castro-Obama meeting might take. Options range from a simple “grip-and-grin” photo, to an historic head-to-head sit down.