MOGADISHU (Reuters) - Somalias al Qaeda-linked rebels struck at the heart of the capital Mogadishu on Tuesday, killing at least 65 people with a truck bomb in the groups most deadly single attack since launching an insurgency in 2007. Witnesses said a truck exploded at the gate of a compound housing government ministries in the K4 (Kilometre 4) area of Mogadishu, where students and parents had gathered to await the results of scholarship exams. We have carried 65 dead bodies and 50 injured people, ambulance coordinator Ali Muse told Reuters. Some are still lying there. Most of the people have burns. Hundreds of parents stood weeping outside the Madina Hospital in Mogadishu after being denied access for security reasons. Reporters were also turned away and nurses said they were overwhelmed with casualties. Al Shabaab insurgents, who claimed responsibility for Tuesdays bombing, pulled most of their fighters out of Mogadishu in August allowing government troops and African Union soldiers to seize much of the coastal capital. But the rebels said they had just changed their tactics and vowed to still carry out attacks on government installations. Paddy Ankunda, spokesman for the African Union force (AMISOM) in Somalia, said students and government soldiers were among the dead. The government said in a statement 15 people had been killed, although diplomatic sources said the death toll was higher, and rising. The government said no senior officials were hurt in the attack. A Reuters reporter saw nine bodies at the compound, which is in an area of the capital under the control of government forces and African Union troops from the east African countries of Uganda and Burundi. The blast destroyed kiosks near the compound and burned the facades of government buildings. Debris from the explosion landed hundreds of meters away. Scores of people with burns were seen walking to a nearby hospital and police were trying to evacuate more students trapped inside the damaged buildings. Muse said it looked as though the truck had been packed with petrol and explosives. He said students, soldiers and civilians were among the dead. Al Shabaab carried out that attack, a spokesman for the insurgents told Reuters. Our target was the ministries. Some analysts said they were worried the attack might prompt some international agencies helping famine victims in Somalia to pull out, leaving operations in the hands of local organisations prone to corruption or theft by militias. Most humanitarian agencies were complaining about lack of security and this might put off international agencies from going anywhere near Mogadishu now, said Hamza Mohamed, a London-based Somali analyst. This is my worst fear now.