Islamabad, Sept 1, SPA -- A loud explosion was heard inthe Pakistani capital on Wednesday, shaking windowsthroughout the city, officials and witnesses said. Thecause of the blast was not clear. The explosion came as the government prepared to swear ina new Cabinet in the capital's heavily guarded presidentialpalace, and just hours after the announcement of the arrestof two al-Qaida suspects in the southwest of the country. Murwat Shah, the police chief in Islamabad's sister city,Rawalpindi, said it was not clear if the explosion wascaused by a bomb. He said he could see smoke billowing froman area between the neighboring cities, which virtuallymerge with each other. "We are trying to find out what caused it," Shah toldThe Associated Press. "From my building I can see smoke." The Interior Ministry said it was aware of the explosionbut had no details. Geo television reported seeingambulances heading toward the Dhamyal military base, nearRawalpindi, but police and security officials said they hadno immediate information about any incident at the base. The air force ruled out a boom from a supersonic jet asthe cause of the explosion.--SPA1337 Local Time 1037 GMT www.spa.gov.sa/197058