Two top Obama administration chiefs have told Pakistan that it has only weeks to show real progress in a crackdown against the country's Taliban, a senior US official said.
The US has put Pakistan "on a clock" to launch a new intelligence and counter-terrorist offensive against the group, which the White House says was behind the Times Square bomb attempt, according to the official.
White House national security adviser James Jones and CIA director Leon Panetta delivered that message to Islamabad last week, said the official.
The high-ranking US delegation presented the Pakistanis with evidence they believe proved that Pakistani-American Faisal Shahzad was trained and funded by the Tehrik-e-Taliban, or TTP, as the Pakistani Taliban is known.
Shahzad is accused of attempting to ignite what turned out to be a poorly-constructed car bomb in Times Square on May 1.
The evidence also showed that two TTP members escorted Shahzad to a training base in the lawless tribal area of Waziristan, where he received some instruction in how to build explosives, the US official said.
Pakistani authorities have already detained two suspects thought to be those TTP escorts, the official said. The US now expects to see Pakistan carry out further independent counter-terrorist operations and quietly increase other unspecified co-operation with the Americans, the official said.
The visiting delegation reminded Pakistani leaders that President Barack Obama had sent them a letter in November, asking for a tougher crackdown against al Qaida and its affiliates like the TTP, the official said.
So far, many US officials have rated Pakistan's progress on that front as mixed because Pakistan has maintained a detente with some of the al Qaida affiliates that operate in its frontier provinces, like the Haqqani network.
The TTP have launched a series of bloody bombings against Pakistani government targets and civilians over the past year.