LAGOS, June 23 (Reuters) - Four foreign hostages employed by oil services giant Schlumberger were released unharmed on Saturday after more than three weeks in captivity, security sources said. The men, from Britain, France, the Netherlands and Pakistan, were abducted on June 1 from the company's residential compound in Nigeria's oil capital Port Harcourt by kidnappers disguised as riot police. "They are unharmed but said they had been threatened during captivity," an official of a private security firm said. More than 200 foreigners have been kidnapped in Nigeria's oil producing Niger Delta since the beginning of last year, and militant attacks have closed about a quarter of the OPEC nation's oil output. Militants who say they are fighting for regional control over the delta's oil wealth have been responsible for some of the violence, but the instability has been exploited by criminal groups and most kidnappings are motivated by ransom.
