A graphic video delivered to The Associated Press on Sunday appeared to show the execution of a Polish engineer by Pakistani militants who had held him captive for more than four months. Pakistan has seen a rash of kidnappings and attacks on foreigners in recent months, mostly blamed on al-Qaida and Taliban militants trying to destabilize the secular government and punish it for supporting the US-led war in neighboring Afghanistan. An American UN worker was abducted last week in the border town of Quetta in southwestern Pakistan. Police said Sunday they were investigating a purported separatist group's claim of responsibility. The seven-minute execution video appears to show the Polish hostage, Piotr Stanczak, sitting on the floor flanked by two masked men. Off camera, a militant briefly engages him in conversation before three others behead him. One of the hooded men then addresses the camera, blaming Pakistan for the execution for not agreeing to their demands to release Taliban prisoners. If confirmed, Stanczak's death would appear to be the first killing of a Western hostage in Pakistan since US journalist Daniel Pearl was beheaded in 2002.