Maryam Abdullahi Gedi, who was among more than 300 people killed in attack, had been due to graduate this week

On Saturday morning, Maryam Abdullahi Gedi made breakfast for her family, packed her books and laptop and set out across Mogadishu, the battered capital of Somalia, to see her supervisor at Banadir University about her thesis. She was excited about the prospect of her graduation as a medical doctor this week.

Her father – who flew in from the UK to attend the ceremony – found himself at her funeral instead. Gedi, 24, was among more than 300 people killed in a massive bombing in the centre of the city on Saturday afternoon.

The death toll from the attack is expected to rise. Rescue workers say the true total of those killed by a truck bomb containing hundreds of kilograms of military grade and homemade explosives will probably never be known. The intense heat generated by the blast, which also ignited a petrol tanker, means that almost no trace of some victims remains. Others were rapidly buried by their relatives, in line with Islamic custom.

“One hundred and sixty of the bodies could not be recognised and so they were buried by the government [on Sunday],” Aden Nur, a doctor at the city’s Madina hospital, said. “The others were buried by their relatives. Over a hundred injured were also brought here.”

Casualties included senior civil servants, five paramedic volunteers and a journalist, but most were ordinary people on one of the busiest thoroughfares of Mogadishu, a city hit by multiple bombings in recent years.

The bomb, which is thought to have targeted Somalia’s foreign ministry, razed buildings across an area the size of three football pitches, witnesses said. At least two people have now been arrested and Somali officials say they are confident they will “trace out the network”.

There has been no claim of responsibility but al-Shabaab, the Somalia-based violent Islamist group is thought to have been behind the attack.

Play Video 1:36 'It was a massacre': witness describes Mogadishu blast – video

A driver of a second smaller vehicle filled with explosives who was detained on Saturday has told interrogators he is a member of al-Shabaab, which means “The Youth”.

“He has told us everything. He is proud of his involvement. He says he did it for jihad,” one security official said.

Funerals continued throughout the day as relatives came to terms with appalling loss.

“I lost the dearest one in my life. They killed my whole hope. I do not know why they killed my daughter … I ask al-Shabaab, ‘Why are you doing this bad on us?’ God help us,” Hinda Yusuf, the mother of Gedi, said.

“My daughter was an extraordinary girl. She was a respectful student. She never confronted anyone in the family. All our neighbours loved her. We called her the ‘lovely one’ due to her good character. I raised her in hardship. After leaving secondary school, she joined the university and it was her ambition to become a doctor.”

After her meeting with her supervisor, Gedi stopped briefly at a maternity hospital, where she had been working as medical student, then called her mother to tell her she was going shopping for clothes with friends for the forthcoming graduation ceremony.

“At around afternoon prayer, I heard the big explosion but being in Mogadishu, where the sound of guns and bombings is part of the life, I was not worried,” Hinda said.

Gedi and her friends were at a clothes shop near the Safari hotel when the blast occurred.

“Around 4pm, I received a call from a relative who told me that my daughter was missing. I dialled her phone number but it was ringing out. I kept trying her then someone, we do not know who, responded and said that the girl died and her body was lying near the entrance of the hotel where the explosion occurred.”

Gedi was buried on Sunday morning at the Barakaat graveyard on the north side of Mogadishu.

Facebook Twitter Pinterest Men and Somali soldiers rescue victims on the site of the explosion of the truck bomb in the centre of Mogadishu. Photograph: Mohamed Abdiwahab/AFP/Getty Images

Another casualty was Mohamud Hassan Elmi, a senior civil servant in charge of humanitarian aid in Somalia. A dual US-Somali citizen, Elmi, 35, was among the many young Somalis who have returned to the country in recent years. Elmi moved to Mogadishu eight years ago after graduating from Ohio State University.

“My brother was humanitarian person. Even in Ohio, he always said he wanted to help the people in Somalia because he saw photos of the hungry people in the country,” Sade Hassan Elmi, a younger brother, said.

Elmi, a father of six, rejected the pleas of his wife and relatives to return to Ohio after a cousin was shot dead in Mogadishu two years ago.

“He said, ‘I would not run away while my work is needed by the people,’” his brother remembered.

The president, Mohamed Abdullahi Mohamed, declared three days of national mourning and joined thousands of people who responded to a plea by hospitals to donate blood for the wounded.

Mohamed, who took power in February, had vowed to rid the country of al-Shabaab. He has faced huge challenges, with the insurgency proving resilient to the ramped-up offensive aided by the US, and a famine.

With reporting by Abdalle Ahmed Mumin in Nairobi