Mystery surrounded the two powerful 'explosions', which were heard on Monday in Islamabad and the nearby garrison city of Rawalpindi, with reports suggesting that they were caused by aircraft breaking the sound barrier.

The loud bangs, heard in the twin cities at about 11 am, rattled the windows of buildings and caused tension among the people.

TV channels initially reported that explosions had occurred within the cantonment area of Rawalpindi and several ambulances were seen rushing to the area.

However, police and emergency services personnel failed to locate the site of the 'blasts'.

They added that all key installations, including the army headquarters, Army House, Presidency and airport, were safe. Reports said that the sounds could have been caused by aircraft breaking the sound barrier over the two cities.