KABUL, Afghanistan (CNN) -- Aid agencies say they will review their presence and security arrangements in Afghanistan after the killing of a foreign relief worker.
Aid worker Gayle Williams was one of 23 expatriates who worked for SERVE Afghanistan.
Gayle Williams, 34, who had dual British and South African nationality, was shot dead on Monday by gunmen on a motorbike in Kabul.
She worked for SERVE Afghanistan (Serving Emergency Relief and Vocational Enterprise), an inter-denominational Christian charity that helps the disabled, the organization's chairman said in a statement.
The Taliban claimed responsibility for the death, saying on its Web site it killed the "foreign woman" for preaching Christianity in the country, adding that it had been following the woman for some time.
Relief charities in Afghanistan, who said in August that attacks on aid workers were forcing them to scale back relief work, said Tuesday that they would look again at increasing protection.
Matt Wilson, deputy program director at War Child, warned that if the situation became more dangerous, then the charity may withdraw its team.
"We are monitoring the situation, and are reviewing whether they need to be in Kabul," he told the UK's Press Association.
"If it became much worse, then we would look at pulling back to somewhere like Turkmenistan and continue our work."
Williams was shot in the western part of the city, Interior Ministry spokesman Zemarai Bashary said, while walking to work. She died shortly after the attack, SERVE Afghanistan chairman Mike Lyth said.
"She was a person who always loved the Afghans and was dedicated to serving those who are disabled," Lyth said. "Needless to say, we are all in shock." Williams was one of 23 expatriates who worked for SERVE Afghanistan, which also employs 450 Afghans in the country.
A statement on SERVE Afghanistan's Web site -- attributed only to "C and E" -- described Williams as "one of the inspiring people of the world who truly put others before herself."
"She was killed violently while caring for the most forgotten people in the world; the poor and the disabled," the statement said. "She herself would not regret taking the risk of working in Afghanistan. She was where she wanted to be -- holding out a helping hand to those in need."
Other charities said they might raise security levels for aid workers. Dominic O'Reilly, UK director of Afghanaid, told PA: "We will review our security, but will continue to use female staff.
"We employ low-profile security and prefer not to use armed guards, but we do review arrangements on a daily basis." He added: "We are a much softer target than the military. Unfortunately I don't think this will be the last casualty."
Christian Aid, said it had no plans to pull its two international staff and a "small" team of local workers out of Afghanistan. A spokesman said: "Arrangements for their safety are kept under constant review.
"We work with local partners where the need is greatest, irrespective of race or religion. "This was apparently accepted by Taliban when they constituted the Afghan government and we were able to work inside the country."
In August British-Canadian aid worker Jacqueline Kirk, 40, and two other women working for the charity International Rescue Committee were killed. And 23 South Korean church volunteers were kidnapped in southern Afghanistan in July 2007. Two were killed before the others were released unharmed.
Journalist Farhad Peikar and CNN's Frederick Pleitgen in Berlin contributed to this report.