KABUL, Dec 5 (Reuters) - An explosion shook the Afghan capital Kabul on Wednesday morning, but it was not clear what caused it and if there were any casualties. The city has been hit this year by a series of suicide attacks by resurgent Taliban, including one targeting a NATO convoy close to the airport on Tuesday. In that attack there were no casualties among the troops, but 22 Afghans were wounded, according to NATO. (Reporting by Sayed Salahuddin, editing by Jerry Norton)
