A rescue worker helps a child outside the Westgate Mall in Nairobi, Kenya Saturday, Sept. 21, 2013, after gunmen threw grenades and opened fire during an attack that left multiple dead and dozens wounded. A witness to the attacks on the upscale shopping mall says that gunmen told Muslims to stand up and leave and that non-Muslims would be targeted. (AP Photo/Khalil Senosi) by Jason Straziuso and Tom OdulaAssociated Press Writer NAIROBI, Kenya (AP) — Kenyan security forces launched a “major” assault late Sunday on the upscale Nairobi mall where an unknown number of hostages are being held by al-Qaida-linked militants, in an operation officials said would end the two-day standoff that had already killed 68 people. The assault, which began shortly before sun down, came as two helicopters circled the mall, with one skimming very close to the roof. A loud explosion rang, far larger than any previous grenade blast or gunfire volley.