Tuesday's blasts, that killed 20 and left over 100 wounded in this ancient holy city, were caused by pressure cooker bombs.

Disclosing this, Uttar Pradesh Police Chief Yashpal Singh told a press conference in Varanasi Friday that the pressure cookers were purchased from a particular shop in the city.

• 2 blasts rock Varanasi; 20 dead

"The pressure cookers and bags inside which the bombs were concealed and abandoned in crowded places were purchased from the local market," Singh said.

This gives a new dimension to the investigations into Tuesday's twin blasts.

Hitherto, officials had presumed that only one bomb was kept in a pressure cooker, that was recovered timely and defused outside a shop in Dashwamegh ghat .

Singh declined to divulge further details of the shops from where the bags were believed to have been bought.

"All I can say is that our sleuths are proceeding on the right trail and it should not take long to zero in on the miscreants and nab them," he added.

While admitting that sketches of suspected bombers released through the media had yet to evoke any concrete response, he said, "The government has, meanwhile, decided to give a cash reward of Rs 100,000 to any one who provides definite clues to their whereabouts."