SANAA (REUTERS) - A suicide bomber drove a car packed with explosives into the gate of Yemen's defence ministry in the capital Sanaa on Thursday causing "a large number of casualties", a source at the ministry told Reuters.

Gun shots were heard near the area as an ambulance rushed to the scene, a Reuters witness said.

Violence is common in Yemen, where an interim government is grappling with southern secessionists, al Qaeda-linked militants and northern Houthi rebels, as well as severe economic problems inherited from veteran President Ali Abdullah Saleh.