A truck bomb exploded outside a hotel in Somali capital Mogadishu, killing 22 people in a heavily secured area close to the presidential palace.A security conference was under way at the hotel on Tuesday at the time of the blast, BBC reported.The Islamist al-Shabab group, which is affiliated to Al-Qaeda, said it is behind the attack.The Somali Youth League (SYL) Hotel is a popular meeting place for government officials and has been targeted by militants before."Security forces tried to stop the bomber who used back roads before he sped through checkpoints near the presidential palace and detonated the bomb," a police officer was quoted as saying."He reached near the gate of the state house with flat tyres."Al-Shabab is fighting to oust Somalia's UN-backed government and establish an Islamic state.