AFP journalists in Islamabad could not access mobile internet services as polls opened at 8 am.
Pakistan suspended mobile phone services nationwide Thursday for election day, the interior ministry said, citing the need to "maintain law and order".
"It has been decided to temporarily suspend the mobile service across the country," a ministry spokesman said in a statement.
The spokesman said "precious lives have been lost" in recent attacks in Pakistan and "security measures are essential to maintain law and order situation and to deal with potential threats".
AFP journalists in the capital Islamabad could not access mobile internet services as polls opened at 8:00 am (0300 GMT), while there were also reports of poor access in the southern city of Karachi.
At least 28 people were killed in twin bomb blasts outside candidates' offices in southwestern Pakistan on Wednesday, in attacks claimed by the ISIS.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)