The president of Somalia has blamed al-Shabab for the country's deadliest attack, in which more than 300 people were killed.

Mohamed Abdullahi Farmajo told Al Jazeera that the armed group's "fingerprints" could be found on Saturday's blast in the capital, Mogadishu, explaining that al-Shabab had a history of similar attacks.

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"This is their fingerprints, this is what they have done," Farmajo said, before calling on the international community to help combat the group.

Al-Shabab has a strong presence in the south of the country.

"If they succeed here, they'll [find it] easier to promote their crazy ideology and their political ideology to the youth in the United States and Europe," he added.

Al-Shabab has not claimed responsibility for Saturday's blast, but the Somali leader had no doubt it was responsible.

"I thought they would claim, but maybe they feel that this is a huge responsibility," Farmajo explained, referring to the scale of the atrocity.

The Somali president's comments come as emergency workers continue to comb through the rubble, looking for the remains of those who died, with officials warning that some bodies might never be found.

Al Jazeera's Mohammed Adow, reporting from Mogadishu, said investigators were trying to find out where the attackers procured the military grade explosives believed to have been used in the attack.

"Another focus, officials say, is whether al-Shabab had help from within the security forces," he said.

The Somali government has been fighting al-Shabab for the best part of a decade and expelled the fighters from Mogadishu in 2011 with help from African Union soldiers.

Al-Shabab has since retreated southwards and continues to hold swaths of territory there.