Addis Ababa - The African Union mission in Somalia's planned withdrawal of 21 000 troops from the extremist-threatened Horn of Africa nation by 2020 cannot be met without urgent help from the international community, the mission's chief said on Saturday.In an interview, Francisco Madeira told The Associated Press he fears all gains made in the past decade could be lost in an abrupt departure.Speaking on the sidelines of an African Union summit, he said the world must "fast-track" to meet the 2020 goal of handing over security responsibilities to Somalia's military. "The UN and other partners must understand that this enterprise needs additional resources," he said.The US military and others have warned that Somalia's forces are not ready as the al-Shabaab extremist group continues to carry out deadly attacks in the capital, Mogadishu, and elsewhere. A truck bombing in Mogadishu in October killed 512 people and was blamed on al-Shabaab's ability to assemble ever-larger explosives. Only a few attacks since 9/11 have killed more people.The US military last year increased its presence in Somalia to more than 500 personnel and carried out more than 30 drone strikes against al-Shabaab and a small presence of Islamic State group-affiliated fighters.But the African Union pullout from Somalia has begun, with 1 000 troops leaving last year. Madeira said he hopes another 1 000 troops will withdraw this year.The AU mission has faced a struggle for stable funding. The continental body says only 40% of its overall budget is funded by its member states, with the balance coming from donors. Observers say the unreliability of outside funding makes it difficult for the AU to finance critical activities such as peacekeeping operations.In 2016 a major funder of the AU mission in Somalia, the European Union, cut its funding for troop allowances by 20%, citing priorities elsewhere in Africa and around the world.Somalia's fragile central government continues to face the challenges of regional tensions and rampant corruption. While President Mohamed Abdullahi Mohamed once vowed to eliminate al-Shabab within a couple of years, his administration has seen multiple shuffles of key security officials in less than one year in office.Earlier this week, the foreign minister of Somalia's breakaway northern territory of Somaliland told the AP that a major cause of Somalia's challenges is its outsourcing of security to others."What Somalia needs to do is to reconcile and engage communities and then to invest in its own security, not to wait and look after others to take care of its issues," Saad Ali Shire said.But the African Union mission head disagreed, saying the long-chaotic nation would have been under al-Shabab control if the foreign forces had not arrived a decade ago.