An explosion in the southern Gaza Strip has killed two Palestinian children. It is not yet clear what caused Friday's blast. Palestinian medics say an Israeli tank shell hit a house near the town of Khan Younis, but Israeli military officials say none of their units in the area was involved. Israeli soldiers say they heard the blast and thought it was caused either by a misfired Palestinian mortar or a prematurely detonated roadside bomb. Some information for this report provided by AFP and Reuters.