New York - UN Secretary General Ban Ki-moon condemned Monday the killing of two aid workers in Somalia and another in Afghanistan in the past three days, saying that he was alarmed by the targeting of people trying to help the poor.

Unknown gunmen shot and killed the head of UNICEF's water and sanitation programme in Somalia on Sunday, three days after an aid worker of the World Food Programme was killed in the central Somali town of Merka.

In Afghanistan, Taliban fighters killed a Western female aid worker for "spreading Christianity" on Monday as she was going to her office in the western part of Kabul.

Gayle Williams, 34, who had dual British-South African citizenship and was working with Serving Emergency Relief and Vocational Enterprises (SERVE), was killed while she walked to work in the Carte Say area of Kabul, police and the aid agency said.

Ban said he was "deeply distressed" to learn of the killings and conveyed his condolences to families, friends and colleagues of the victims.

"The secretary general deplores these acts of deliberate violence against those who are making every effort to alleviate the dire suffering of Somali and Afghan citizens," Ban said in a statement.

He said he was alarmed by the increasing trend of killing and abduction of aid workers in both countries.

Ban called on "all parties to respect the neutral and impartial status of humanitarian staff, to allow them to do their work bringing vital life-saving assistance to the millions of Somalis and Afghans who are counting on this support for their survival." (dpa)