Mogadishu - A car bomb critically injured a university lecturer in Somalia's capital Mogadishu on Wednesday and was blamed on Islamist rebels who have promised to keep up attacks even as they have lost territory to a military offensive.There was no immediate claim of responsibility by the al-Shabaab group but it has often used such devices. An al-Shabaab car bomb killed four people in Mogadishu on Sunday."It was a planted bomb probably controlled remotely," police captain Isa Ahmed told Reuters, blaming al-Shabaab for the Wednesday's blast. It was not clear whether the bomb had targeted the lecturer, he said.A source at Madina hospital said the man, a lecturer at Mogadishu's SIMAD University, was in a coma and in a critical condition.Hit-and-run attacksAl-Shabaab has been driven out of its main strongholds in southern and central Somalia by African Union peacekeeping forces and Somali troops.But analysts say the group still has the capacity to wreak havoc with hit-and-run attacks and to hinder the Western-backed government's efforts to restore order to a nation that is struggling to rebuild after more than two decades of war.In the northern, semi-autonomous Puntland area, regional President Abdiweli Mohamed said 20 al-Shabaab rebels and five soldiers have been killed in fighting in the past week in the Galgala hills, an area Puntland previously said it controlled."The battleground is now in our hands," the president told reporters on Tuesday.Al-Shabaab's military spokesperson, Sheikh Abdiasis Abu Musab, said the group had killed 23 soldiers in three days of clashes and said the fighting was continuing.Rebels and officials often give different accounts and death tolls.