SANA, Yemen — A masked gunman assassinated a Yemeni security official who worked for the US Embassy in a drive-by shooting Thursday near his home in the capital, officials said, adding that the assault bore the hallmarks of Al Qaeda’s Yemen branch.

The attack comes amid a sharp deterioration of security in Yemen and several other Muslim countries since the collapse of police states controlled by autocratic leaders during a wave of uprisings known as the Arab Spring.