Three persons were killed yesterday in the explosion near the venue of the poll campaign of Congress candidate Harminder Singh Jassi at Maur Mandi.
"One more child has succumbed to injuries at CMC hospital in Ludhiana," Bathinda Deputy Commissioner Ghanshyam Thori said today, adding, the victim has been identified as 13-year-old Saurabh Singla.
Earlier, Ripandeep, 9, and Japsimran, 14, died at the CMC hospital where they were admitted. Thirteen injured - three of them critical - are undergoing treatment at different hospitals.
Punjab DGP Suresh Arora along with other senior police officials today inspected the blast site. He said it was an "unfortunate incident".
Mr Arora said the Home Ministry has been requested to send experts of NSG to identify the material used in the explosion.
Asked whether the IED was used to carry out the blast, the DGP said one pressure cooker exploded in this incident while another was found at the spot. A forensic team has reached the site to probe the matter, he said.
On "terror angle", he said, "Stating that this (terror) angle is not possible, it will be wrong to say at this moment. We are not ruling this possibility."
Meanwhile, the Election Commission has sought a report from Punjab Police on the car explosion.
Chief Minister Parkash Singh Badal condemned the blast and urged people to exercise calm and said those involved in it would be dealt with severely.
"Nobody would be allowed to disturb the hard-earned peace and communal harmony in the state," he had said earlier in the day.
AAP convener Arvind Kejriwal demanded immediate arrest of SAD chief and Deputy Chief Minister Sukhbir Singh Badal to ensure peaceful elections.
"To ensure peaceful elections, Sukhbir Badal should be immediately arrested. His role in yesterday's blast be probed. He'll cause more violence," Kejriwal tweeted.
Meanwhile, Congress Punjab chief Amarinder Singh blamed Mr Kejriwal for the explosion alleging that he had been promoting extremist forces like Khalistan Commando Force in the state.