A car laden with explosives blew up in front of the Ministry of Education in the Somali capital Tuesday, killing 55 people in the biggest attack since a militant insurgent group withdrew from Mogadishu, a rescue official said.

At least 30 others were injured, Ali Muse, the chief of Mogadishu’s ambulance service, told The Associated Press.

Ali Hussein, a police officer in Mogadishu said the vehicle blew up after pulling up to a checkpoint at the entrance to the ministry offices.

The al Qaida-linked militant group al-Shabab immediately claimed responsibility for the attack on a website it uses.

The blast has shattered over a month of relative calm in Mogadishu. Al-Shabab withdrew from the city in August amid an offensive by African Union forces, and as victims of a famine in the south began flooding into the city.

Al-Shabab is waging an insurgency against the weak UN-backed Somali government.