Gunmen in Yemen have seized the president's chief of staff. Ahmed Awad bin Mubarak and two of his guards were abducted early on Saturday in the heart of the capital Sanaa.Yemeni officials suspect Shia Houthi rebels, who control much of the capital, of being behind the abduction. One source said Bin Mubarak was nabbed by the Houthis to stop him from presenting a draft of the new constitution to a presidential meeting. The rebels blocked his appointment as prime minister last year.