The top U.N. envoy in Somalia warned Wednesday that warlords are likely to fill the vacuum created by the departure of al-Shabab Islamist fighters from the capital unless the government takes immediate action to promote law and order, AP reported. Augustine Mahiga told the U.N. Security Council in a videoconference briefing from Mogadishu that al-Shabab's recent and unexpected withdrawal from the city presents the first opportunity in years for the transitional government to exercise authority over the capital. If this is managed effectively, he said, it will "expedite political gains" and the delivery of humanitarian aid to thousands of Somalis fleeing famine and arriving in Mogadishu. Somalia has not had an effective government since 1991, when warlords overthrew a longtime dictator and then turned on each other, plunging the country into chaos and anarchy. A transitional government, established in 2004 and currently backed by about 9,000 African Union troops, has been fighting against al-Shabab insurgents. Al-Shabab controlled around a third of Mogadishu until Saturday morning when its fighters suddenly withdrew from all their bases in the capital. They still hold most of southern Somalia, where tens of thousands are estimated to have starved and tens of thousands more are trying to reach the capital in hopes of finding food. -- SPA