A suspected separatist group that has been holding an American UN worker in Pakistan for a month said it would kill him in four days if the government does not release more than 1,000 prisoners. The threat on the life of John Solecki was made in a letter sent Sunday to local news agency Online International News Network that was also read by an Associated Press reporter. The group said February 13 that it would kill Solecki within three days unless similar demands were met, but apparently did not follow through. UN spokeswoman Maki Shinohara said the world body was aware of Sunday's threat through news reports and "took it seriously." Gunmen seized Solecki on February 2 after shooting his driver to death as the pair drove to work in the southwestern city of Quetta in Baluchistan.