CAIRO - Hosni Mubarak, who ruled Egypt for three decades until overthrown by a revolution in the "Arab Spring" last year, was declared clinically dead by his doctors on Tuesday, the state news agency MENA said in a report confirmed by a hospital source.Mubarak was 84 and had been sentenced to life in prison earlier this month."Former president Hosni Mubarak has clinically died following his arrival at Maadi military hospital on Tuesday evening," MENA said, quoting medical sources."Mubarak's heart stopped beating and was subjected to a defibrillator several times but did not respond."Two security sources denied the report, saying Mubarak was unconscious and on a respirator but not clinically dead."It is still early to say that he is clinically dead," a military source told Reuters.