The Oxfam aid organisation has temporarily closed two of its offices in Sudan's troubled Darfur region after the abduction of a Sudanese employee.
Oxfam says it has taken steps to ensure needs are met
The man was seized by gunmen who hijacked an Oxfam vehicle two months ago and remains missing.
Oxfam says the hijacking and looting of aid vehicles has steadily increased in Darfur in recent months.
The region's three-year conflict has left more than 200,000 people dead and two million displaced.
Oxfam says increasing insecurity is making it ever more difficult and dangerous for aid agencies to operate.
It called on the international community to do more to support the 7,000-strong African Union peacekeeping mission there.
The two offices that have been closed - Saraf Omra and Birka Seira - are in North Darfur.
Oxfam's programmes in the surrounding villages and camps for the displaced have been providing more than 50,000 people with clean water, sanitation facilities, hygiene education and assistance to improve their livelihoods.
Oxfam says it has taken steps to try to ensure that many needs will continue to be met.
Paul Smith-Lomas, Oxfam's regional director, said: "Since the abduction we have been working tirelessly with the African Union, the UN, government authorities and local communities to try and locate him, without success."
Rebel forces took up arms in Darfur in February 2003, accusing the government of discriminating against black Africans in favour of Arabs.
Although a peace deal was agreed two months ago, only one of the rebel groups signed it and all the deadlines for implementing the agreement have so far been missed.