Three American doctors have been shot dead in Yemen by a lone gunman - described as a suspected Islamist , BBC reported. A fourth was wounded in the attack in the southern town of Jibla, hospital sources told the AFP news agency. The fire was opened with a Kalashnikov assault rifle at a Christian-run hospital in the province of Ibb, about 170 kilometres (105 miles) south of the capital Sanaa. The US believes al-Qaeda members went into hiding in Yemen after the collapse of the Taleban in Afghanistan last year. Last month, an unmanned aircraft operated by the US Central Intelligence Agency (CIA) targeted and killed six al-Qaeda suspects in Yemen. In March, there was an explosion outside the US embassy in Sanaa - a day after US Vice President Dick Cheney visited the country.