Palestinian militant groups threatened Thursday to abandon a fragile cease-fire after Israeli undercover troops shot and killed a wanted Palestinian militant in a West Bank refugee camp. A series of incidents over the last week has frayed the relative calm that took hold after the election of Palestinian Authority President Mahmoud Abbas in January. Last weekend, Israeli troops shot and killed three Palestinian boys under disputed circumstances in the southern Gaza Strip. Palestinian militants responded with a rain of mortar shells against Jewish settlements. No casualties resulted. Full Story