Somali al Shabaab group says Kenya can't act on its threats By Feisal Omar MOGADISHU (Reuters) - The Somali Islamist militant group Al Shabaab taunted Kenya on Sunday as its guerrillas awaited a government bid to end a siege in the Nairobi shopping mall they had seized a day earlier. Al Shabaab has claimed responsibility for the attack, in which 59 people were confirmed killed and a further undisclosed number were being held hostage on Sunday. Kenyan President Uhuru Kenyatta pledged to clear out the attackers and track the planners down. In an address on Sunday, he promised to punish the masterminds "swiftly and painfully." Where will Uhuru Kenyatta get the power with which he threatened us? Sheikh Abdiasis Abu Musab, Al Shabaab's military operations spokesman, told Reuters in Somalia. His forces are the weakest in Africa. We have been fighting Kenyan forces for two years ... If Uhuru wants peace from us, he should withdraw his troops from Somalia. Shortly after he made his comments, Kenyatta told a news conference that Kenya would not relent on its "war on terror" in Somalia, where its troops and other African peacekeepers are fighting Islamist militants including al Shabaab. The Kenyan government had said there were 10 to 15 attackers in Nairobi, and that they had been isolated in one area of the mall. Abu Musab declined to divulge details of the attackers or their hostages. Instead he taunted Kenya for seeking support from Israel, after an Israeli security source said Israeli advisers were helping Kenya to formulate a strategy to end the siege. Addressing Kenya's leader, Abu Musab said: "Uhuru, threatening and bluffing are nothing, take your own AK-47 (rifle) and meet us at the frontline." Additional reporting by Abdi Sheikh; Writing by Edmund Blair in Nairobi