(Adds details) KABUL, April 1 (Reuters) - An explosion shook the Afghan capital on Sunday, but it was not clear what caused it and if there were any casualties, residents said. Kabul has been hit by several suicide attacks by a resurgent Taliban in recent months as part what is regarded as the start of the expected spring offensive by the militants. Police said they were checking. Foreign forces are bracing for a new offensive by the Taliban after 2006 saw the bloodiest fighting since the rebels were ousted from power in 2001.
