Somali President Sheikh Sharif Ahmed on Tuesday declared three days of mourning and vowed to put in place security measures to avert future bombings after Al-Shabab Islamist insurgents attacked Mogadishu.
His government is supported by some 9,000 African Union peacekeepers but they only control the capital.
"I'm sure the crime they committed against the Somali people will not go unpunished," he said of Al-Shabab militants. "God will punish them and the government will take appropriate measures to save the Somali people from those dangers."
A truck loaded with drums of fuel exploded on Tuesday outside the Ministry of Education on one of central Mogadishu's busiest streets, where students and their parents were registering for scholarships offered by the Turkish government. It was the deadliest single bombing in Somalia by the Islamist insurgents.
Al-Shabab immediately claimed responsibility for the bombing, saying it was striking government officials and foreigners—referring to AU peacekeeping troops supporting the UN-backed government.
"It shows their barbarism and how hell-bent they are to hit the public where it hurts most," he said. "We can certainly say their ideology is directed at annihilating Somali people. What they're targeting is the education."
The UN Security Council called the attack a "heinous crime."
In Washington, White House press secretary Jay Carney said it was a "despicable and cowardly act."
Although the Islamic fighters made what they called a "tactical withdrawal" from their bases in Mogadishu amid an AU offensive in August, they had vowed to carry out devastating suicide attacks.
The thunderous blast covered the city in dust more than a half-mile (800 meters) away and left blackened corpses sprawled amid burning vehicles. One woman used a blue plastic bucket to pour water on a charred and smouldering body.
Rescuers rushed scores of victims with burns and severed limbs to Medina Hospital, said nurse Ali Abdullahi. Even in a city beset by war and anarchy for two decades, the bombing horrified medical workers.
"It is the most awful tragedy I have ever seen," said the nurse. "Imagine, dozens are being brought here minute by minute. Most of the wounded people are unconscious and others have their faces blackened by smoke and heat."
Duniya Salad sobbed over her brother's burned body after he died while undergoing treatment. “They killed him before he started university! Why was he killed? Damn to Al-Shabab," she said.
At least 70 people were killed and 42 wounded, said Ali Muse, chief of Mogadishu's ambulance service.
"The explosion has not only affected the targeted place, but even passers-by and car passengers died there.
“The death toll may increase and we are still carrying many dead bodies," he said. "It is the worst tragedy I have ever seen in the capital."
Major General Fred Mugisha, the commander of the African Union Mission to Somalia force, known as AMISOM, said the attack targeted several Somali government institutions.
The suicide bomber detonated the explosives after the vehicle rammed a checkpoint outside a compound housing several government ministries, Mugisha said.