An American woman has been shot dead in the port city of Sidon in southern Lebanon.

Police said the woman, a missionary, was found dead in a building that houses a chapel and a clinic in a southern district of the city.

The victim, named as Bonnie Witherall, worked as a nurse in the building - she was found with at least one bullet to the head.

Police said an unidentified gunman knocked on the door of the clinic at around 0800 (0600 GMT) and shot Weatherall, the Associated Press reported.

The killer fled and the motive for the shooting was not known, police said.

However, a police source quoted by Associated Press says the crime probably stemmed from anti-Americanism.

"This was apparently an act committed by a person filled with anti-American feelings in the generally hostile climate toward the US, which people here reproach for its desire to carry out a war against Iraq and for supporting Israel," said the official.

The US Embassy in Lebanon said the incident was being investigated.

It is the first killing of an American citizen in Lebanon in more than 10 years.

Reports say Witherall had worked for the Evangelical mission in Sidon for the past eight years.