"Today's attack highlights the repugnant terrorist tactics al- Shabaab continues to use to stand in the way of efforts to ease the suffering of the Somali people," White House National Security Council Spokesperson Caitlin Hayden said in a statement.

　　The statement came after suicide bombers attacked the UN's office in Mogadishu, Somalia's capital, on Wednesday, leaving at least 15 people dead, including eight working for the UN. The al- Qaida linked militant al-Shabaab group said it was behind the assault.

　　"Whether by denying food and medical aid during one of the region's worst droughts, or by repeated attacks against fellow Somalis and soldiers helping to build a lasting peace, al-Shabaab has shown again and again that it stands on the side of death and destruction," Hayden said.

　　Hayden also reiterated Washington's support to the United Nations in building a safer and more prosperous future of Somalia.

　　The deadly Mogadishu attack comes at time when the new UN mission for Somalia known as UNSOM have taken over from the previous mission whose mandate ended in June.

　　The radical group of al-Shabaab has previously banned UN aid agencies from operating in areas under their control accusing the agency of carrying out anti-Islam activities, a charge vehemently denied by the world body.

　　UN Secretary-General Ban Ki- moon on Wednesday told the Somali president that he was "concerned and outraged" by the attack.