MANILA, Philippines — A powerful explosion ripped through a passenger bus in the Philippine capital on Tuesday, killing at least two people and wounding at least 18 others, officials said.The explosion was so powerful that it punched a hole in a nearby concrete fence along metropolitan Manila's main highway in suburban Makati city, Mayor Junjun Binay said.The bus was approaching a commuter railway station when the blast occurred inside the vehicle, taking out half of its front windshield, punching holes in windows and immediately killing a female passenger near the center of the explosion, Binay said.He said the damage indicated that it was caused by a bomb.He said one hospital reported two people dead and 18 wounded.