The Pentagon on Thursday said Pakistan would decide when to move against extremists in North Waziristan and that it was not Washington's role to dictate timing of military operations in the country.
US officials have long urged Pakistan to take its offensive against Islamist militants to North Waziristan, home to an array of extremists including Al-Qaeda and the so-called Pakistani Taliban.
Revelations that a foiled car bomb plot in New York City may have been linked to the Pakistani Taliban have added fresh urgency to US requests for action by Islamabad in North Waziristan.
Pentagon press secretary Geoff Morrell repeated the administration's view that the Pakistan army had made major progress against militants over the past year, saying Washington is "fully supportive of their efforts."
Asked about North Waziristan, Morrell said: "There are safe havens that have yet to be fully targeted, as aggressively targeted as can be, as needs be.
"But the pace and the timing and the schedule to undertake those operations is of the Pakistanis' choosing."
He said US and Pakistani officials investigating the car bomb plot were "exchanging information" and that Islamabad had promised to cooperate.
A Pakistani-born US citizen, Faisal Shahzad, is accused of planting a large but poorly made car bomb in crowded Times Square on Saturday.
US authorities arrested Shahzad late Monday and were continuing to question the suspect, trying to determine whether the 30-year-old son of a retired Pakistani air force officer acted alone or had outside help.
Despite the amateurish attempt, Shahzad allegedly has admitted having received "bomb-making training" in Pakistan's lawless Waziristan region.
The Pakistani military has said its forces are stretched fighting extremists elsewhere and are not yet ready to stage an operation in North Waziristan.
The CIA frequently bombs militants in North Waziristan using unmanned aircraft.