MICHAEL GEORGE and ELLEN FRANCIS LEBANON's president says its investigation into the biggest blast in Beirut's history would examine whether it was caused by a bomb or other external interference, as residents sought to rebuild shattered homes and lives. Rescuers sifted rubble in a race to find anyone still alive after Tuesday's port explosion that killed 154 people, injured 5,000, destroyed a swathe of the Mediterranean city and sent seismic shockwaves around the region. "The cause has not been determined yet. There is a possibility of external interference through a rocket or bomb or other act," President Michel Aoun told…