The world's longest serving Prime Minister, Prince Khalifa bin Salman Al Khalifa of Bahrain, passed away yesterday. He was 84.<br />'' <br />''Prince Khalifa, who took office after Bahrain gained independence in 1971, had been receiving treatment at a hospital in the US, the state media said. He was an uncle to the Bahraini King Hamad Bin Isa Al Khalifa.<br />'' <br />''<span style="color: #222222;">A week-long official mourning has been declared in Bahrain and flags will be flown at half-mast. Government ministries and departments will be closed for three days starting this morning.</span><br />