Mogadishu - A car bomb exploded in Somalia's capital, killing at least eight people and injuring 15, police said Wednesday, as the extremist group al-Shabaab quickly claimed responsibility.The Somalia-based group has vowed to step up attacks in Mogadishu and elsewhere after the federal government recently announced a new offensive against the group. Targets have included high-profile spots like military facilities, hotels and areas close to the presidential palace.The car with explosives had been parked outside a restaurant near the city's port, Captain Mohamed Hussein told The Associated Press. Among the dead were a mother and child who were at the restaurant, he said."We would ask Allah to give his mercy on their souls," said Abdifitah Halane, spokesperson for Mogadishu's mayor.Al-Shabaab last year became the deadliest Islamic extremist group in Africa, with more than 4 200 people killed in 2016, according to the Washington-based Africa Center for Strategic Studies.Somalia's military is under growing pressure to assume more responsibility for the long-chaotic country's security as a 22 000-string multinational African Union force plans to start withdrawing next year.The prospect of a security vacuum has concerned the international community. Somalia's president has urged that the UN arms embargo on his country be lifted soon, saying the military needs more than AK-47s to combat al-Shabaab and the small but growing presence of Islamic State-linked fighters in the north.President Mohamed Abdullahi Mohamed, a Somali-American who was elected in February, has repeatedly said al-Shabaab can be defeated within two years, but he warns that could take much longer without a better-equipped national military.On Tuesday, the national police chief in neighbouring Kenya said al-Shabaab attacks had increased in that country as the extremist group faces growing pressure from the AU force in Somalia.