Nokia has identified a problem with one of its 3rd-party supplied phone chargers and has initiated a free replacement service.
Chargers manufactured by a third party have problem with its plastic that opens up as you use & exposes internal components. This might lead to electric shock when touched.
Only a limited number of chargers of certain model types manufactured by a single third-party supplier during a specific time period are within the scope of the exchange program. They are the AC-3E and AC-3U models, manufactured between June 15, 2009 and August 9, 2009; and the AC-4U model, manufactured between April 13, 2009 and October 25, 2009.
For more information, including how consumers can check to see if their chargers need a replacement or not, Nokia has established a website http://chargerexchange.nokia.com to figure out the status.
Also you can go to Nokia Care Shops to get advise on it, you may find this link useful to find out Nokia Shops in your city (in Pakistan)
Nokia has said that it is not aware of any incidents or injuries related to these chargers.