US Ambassador Richard Olson said Washington was ready to help Pakistani authorities investigating the on Saturday incident that left around 60 people dead.
"On behalf of the American people, I extend my heartfelt sympathies and condolences to the families of the victims as well as to the government and people of Pakistan," Olson said in a statement.
He said the attack "demonstrates terrorists' blatant disregard for life".
"We support Pakistan's efforts to bring all those involved in planning and executing this attack to justice and stand ready to provide any appropriate assistance to authorities investigating this tragic attack," he said.
Meanwhile, an improvised explosive device (IED) was on Monday found in the parking area of Pakistan's Wagah border.
The Bomb Disposal Squad seized the IED and then searched the area surrounding the border. Security forces also searched nearby villages and rounded up several suspects, The Nation reported.