Pakistani police are investigating a purported separatist group's claim to be holding a kidnapped American UN worker, an officer said Sunday, a day after Islamist militants close to the Afghan border said they had killed a Polish geologist. Pakistan has seen a rash of kidnappings and attacks on foreigners in recent months, mostly blamed on al-Qaida and Taliban militants seeking to destabilize the secular government and punish it for supporting the US-led war in neighboring Afghanistan. American John Solecki was seized last Monday in Quetta in the southern Pakistan province of Baluchistan as he drove to work at the offices of the UN refugee agency there. Quetta's chief investigator Wazir Khan Nasir said a previously unknown ethnic Baluch separatist group called the Baluchistan Liberation United Front telephoned a local journalist Saturday to claim responsibility. He did not say what the group's demands were. The natural-gas-rich region is home to a decades long insurgency, but foreigners had never been targeted previously. "We are vigorously looking into the matter," Nasir told the AP.