Three people were wounded when gunmen fired a barrage of mortars that landed inside the main United Nations base in Somalia's capital Mogadishu, the UN said on Tuesday."Seven mortars landed inside the compound this afternoon, injuring two UN staff members and one contractor," the UN said in a statement. "None of the injuries is life-threatening."The Islamist group al-Shabaab claimed responsiblity for the attack.The Shabaab, an al-Qaeda affiliate, is fighting to overthrow the internationally backed Somali government in Mogadishu.Such attacks used to take place nearly daily, but have declined since the Shabaab fled fixed positions in the capital in 2011.They still control parts of the countryside and carry out attacks against government, military and civilian targets seemingly at will in both Mogadishu and regional towns."No political agenda can be served through violence that deliberately targets staff members of international organizations who are supporting the consolidation of peace and the strengthening of governing institutions in Somalia," said Nicholas Haysom, the head of the UN's mission in the country.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.