Yemeni President Ali Abdullah Saleh, whose compound was attacked today, appears unable to shut down the unprecedented challenge to his 32-year rule.
Yemen's Houthi rebels claim a Saudi Arabia air strike on Sunday killed 54 people, including women and children. The US is increasingly concerned restive Yemen is becoming a haven for terrorism.
Four clashes in the past eight days underscore the state's vulnerability. Southern secessionists and northern rebels have weakened the central government.