By Abdrahman Hussein and Ismail Taxta MOGADISHU (Reuters) - Somalia's parliament on Monday sacked Prime Minister Abdi Farah Shirdon, citing his government's poor performance over the past year. The prime minister, a political newcomer appointed in October last year, fell out with President Hassan Sheikh Mohamud over the composition of a new cabinet, prompting Monday's no-confidence vote. Analysts and diplomats said a replacement must be appointed soon to end political paralysis after two decades of war and chaos in which the Horn of Africa state was carved up into clan fiefdoms and then ruled by al Shabaab militants. Western donors had worried the rift would disrupt efforts to shore up nascent institutions of state and defeat Islamists linked to al Qaeda who still control swathes of countryside. " (Shirdon) and his cabinet ministers had failed," Somali legislator Ibrahim Suleiman told Reuters. This toppled government had low capacity. It could be months before a new cabinet is appointed and then approved by the parliament, which could jeopardize the modest security gains and the limited progress made on building a federal state. "This is going to disorient the entire political structure," said Abdi Aynte, director of Mogadishu-based Heritage Institute for Policy Studies. President Mohamud had told Western diplomats the bid to remove Shirdon was prompted by the government's poor performance, made worse by growing discontent among Somalis who want faster progress on delivering change. "Prime Minister Shirdon in many ways has become a scapegoat for a relative lack of progress - particularly measured against the huge expectations - since the government came to power," said Paul Gabriel, an analyst for Global Risk Analysis. While progress has been made to bring Somalia back into the international fold and attract greater donor funds, many ordinary Somalis say their lives remain mired in poverty and violence while political corruption continues unabated. The political turmoil also follows a row about corruption related to the central bank. Mohamud's task of picking a new premier will also be made harder by Somalia's volatile clan dynamics. Nick Kay, the U.N.'s Special Representative to Somalia, said Mohamud must act quickly. "It is in all our interests that the next PM and government is broadly inclusive, able to unite the country and capable of delivering what Somalia needs - peace, rule of law, economic growth and good public services," Kay said in a statement. The Somali public viewed Shirdon as a weak politician but the former academic said he stood up to President Mohamud about too much power in the cabinet being wielded by Damul Jadid, a powerful Islamist faction which counts the president as a member and has links to Egypt's Muslim Brotherhood. "I clearly told the president that it was unfair to leave Somalia in the hands of a group with a particular interest," Shirdon said. Legislators close to the prime minister said that was a reference to Damul Jadid. One Western diplomat said the international community wants Mohamud to appoint a strong prime minister. But analysts said he could take the opposite route and appoint a prime minister with little political clout, thereby increasing his own influence and power within Somali politics. "This carries the risk of unsettling the carefully crafted clan balance that allowed for the political progress seen in 2012," analyst Gabriel said. Additional reporting by Abdi Sheikh, Writing by Drazen Jorgic, Editing by Angus MacSwan