At least 65 people were killed when a truck bomb went off outside a hotel and market in the centre of the Somali capital of Mogadishu, security officials told EFE on Sunday.The bombing attack, which took place on Saturday, was the most deadly attack to have hit the Horn of Africa country in three decades, leaving an undetermined number of casualties which could lead to an increase in the death toll in the coming hours.Most of the victims were civilians, according to local media outlets.Meanwhile, the International Committee of the Red Cross confirmed on Twitter the deaths of five Somali Red Crescent volunteers in the attack."This figure may rise as there are a number of volunteers still missing," the ICRC said in a statement.Somalia's President Mohamed Abdullahi Farmajo declared three days of mourning and called on the public to help victims by giving blood.The city's inhabitants were continuing to search for victims under the rubble of buildings that were damaged by the blast."I lost my three brothers in the attack, we were at our pharmacy when it happened," Mohamed Abshir, who survived the attack, told EFE.No group has claimed responsibility for the attack, but local media outlets have pointed to Somali terror group al-Shabaab as likely behind it.Al-Shabaab, an Islamist group affiliated with the al-Qaida terrorist organization, is seeking to establish an Islamist state in Somalia and occupies swathes of territory in the African nation.