GENEVA (Reuters) - Sadako Ogata, the U.N. High Commissioner for Refugees, on Tuesday strongly condemned the abduction of a French aid worker 12 days ago in southern Russia and demanded the staff member's immediate release. In an appeal issued in Geneva and Moscow, she said the agency had "temporarily suspended" its relief operation based in Vladikavkaz, North Ossetia, since the abduction due to security concerns. But staff have remained in Vladikavkaz, the UNHCR's base for aiding 100,000 refugees and displaced people in the region comprising Chechnya, Georgia, Ingushetia and North Ossetia. Vincent Cochetel, head of the UNHCR's office in Vladikavkaz, capital of North Ossetia, was kidnapped on the night of January 29 from his apartment by three masked gunmen. His local driver, the only witness to the abduction, had been detained by authorities since the incident, but was released on Monday, according to Kumin. Ogata, in an appeal issued in Geneva and Moscow, said she was "profoundly concerned" by the continued detention of the 37-year-old Cochetel. No one has yet claimed responsibility. "The increasing threats to aid workers, whose only aim is to alleviate the suffering of innocent people, puts the very foundation of humanitarian work at risk," she said. Hostage-taking has become rife in North Ossetia, which is close to Russia's breakaway Chechnya republic, since the last Russian troops withdrew from Chechnya in humiliation last year after a disastrous 21-month battle with Chechen separatists.