Two Afghan aid workers employed by a German non-governmental organization were killed when armed men attacked their car in the southeastern province of Khost, U.N. officials said on Wednesday. Mohammad Nadir Farhad, a spokesman for United Nations High Commission for Refugees (UNHCR) told Deutsche Presse Agentur dpa that the incident occurred late Tuesday afternoon in Zurmat district of Khost. The two aid workers were working for MALTESER, a German NGO in Khost province, Farhad said. The field officer of the NGO was killed on the spot and the driver, who had been seriously injured, was first transferred to Bagram hospital, 50 kilometers north of Kabul, and died later. "We are extremely concerned about the repeated security incidents involving aid workers," Farhad said. Following the incident, Farhad said, MALTESER completely suspended its operation in southeastern region. Farhad, however said the UNHCR will continue to provide emergency relief to some 20,000 Afghan returnees who have recently returned home from south Waziristan of Pakistan. In Afghanistan, MALTESER was being funded by UNHCR to perform specific projects such as vocational training and cash for work in Khost province, according to Farhad. No one has so far claimed responsibility, but in the past, Afghan authorities have blamed ousted Taliban members for similar attacks.