Mogadishu, Somalia (CNN) -- A Somali lawmaker was killed and another was injured when a bomb hidden in their car exploded while they were headed to a conference on security, officials said.
Parliamentarian Isack Mohamed Ali, popularly known as Isack Rino, was killed, and lawmaker Mohamud Abdi-dhuuh was seriously injured, said Mohamed Abdiqadir Mohamed, district commissioner of Mogadishu's Hamarweyne district. Four passersby were also hurt.
The parliamentarians were on their way to a national conference on security when the bomb, hidden under one of the car's seats, exploded.
The Islamist rebel group Al-Shabaab claimed responsibility for Monday's bombing in a statement posted to a pro-militant website.
Prime Minister Abdiweli Sheikh Ahmed said those behind the "cowardly" attack would be found.
"Somalia has today lost a committed parliamentarian who worked tirelessly to serve the people of Somalia and help rebuild our country," Ahmed said in a statement.
"This cowardly attack will not derail the progress made in Mogadishu and across Somalia. The security agencies will investigate this cowardly killing and ensure that those who carried out this attack face justice."
Journalist Omar Nor reported from Mogadishu; CNN's Holly Yan wrote from Atlanta. Tara Kangarlou also contributed to this report.