At least seven persons were killed and several others injured in the southern Pakistani city of Karachi on Friday when a blast ripped through a house where explosives and weapons were stored.
The blast in Baldia Town area of the port city appeared to be accidental and bomb disposal squad personnel were trying to determine its exact nature, police officials said.
Two Kalashnikov assault rifles, 22 grenades and two suicide jackets were found in the one-room house, which collapsed due to the explosion.
Interior Minister Rehman Malik told media persons in Islamabad that the home had been rented by a man from the militancy-affected Swat valley.
Some persons from Swat had come to visit this man on Thursday night, he said.
Police officials said Riaz Khan, who hailed from Swat, had rented the house about two years ago. They said two grenades were found in the pocket of one of the dead. Two suspects were arrested from the scene, they said.
Karachi police chief Waseem Ahmed told the media that the men living in the house could have been planning a terrorist attack.
The explosion damaged windows of several homes in the congested neighbourhood.
Rescue workers sifted through the rubble of the house and pulled out the bodies and injured after security forces cordoned off the area.
Interior Minister Malik said a crackdown would be launched against illegal migrants living in cities like Karachi and the government would show "no mercy" to elements involved in militancy and extremism.
He also warned foreigners, including Afghan nationals, living illegally in Pakistan to leave the country.
In a statement, Prime Minister Yousuf Raza Gilani expressed concern that the storage of explosives in a residential area of Karachi had "remained unnoticed by the law enforcement agencies".
He ordered an inquiry into the incident and directed authorities to immediately submit a report to him.