The early morning blast, as traders assembled for fruit auctions, left severed body parts and bloodstained clothes scattered throughout stalls at the market on the border between the capital Islamabad and its twin city of Rawalpindi.

Police said the bomb had been hidden in a box of guava fruit.

"Body parts went everywhere and even hit other people on the head," said Shaheen, a worker who only gave one name.

At the site, bloody sandals lay amid boxes of straw and damaged fruit in the mud. Police waved metal detectors haphazardly over boxes while dazed fruit sat amid the wreckage.

Shopkeeper Gohar Khan said that he had seen around 15 bodies.

"Human remains, blood was strewn all over the area," he said.

Dr. Javed Akram Qazi, vice chancellor of the Pakistan Institute of Medical Sciences, confirmed that their hospital had received 18 bodies. He had been notified by police of five more deaths and more wounded were arriving, he said.

Police said at least 39 people had been wounded.

Rawalpindi, whose suburbs blend into the capital, is the site of the powerful Pakistani military's headquarters. But the blast occurred far from army buildings and the purpose of the attack was unclear.

There were no immediate claims of responsibility. Pakistan is holding peace talks with the Pakistani Taliban insurgency, which is supposed to be observing a ceasefire until April 10, but there are dozens of other militant groups.

The Taliban are demanding the release of hundreds of prisoners and the withdrawal of the army from some of the tribal areas along the border with Afghanistan.

The Taliban are fighting to overthrow Pakistan's democratically-elected government and impose a strict form of Islamic law.