Reporting from Washington — Senior U.S. officials used an urgent meeting with Pakistan's president to present a dossier on terrorism suspect Faisal Shahzad, including a detailed chart describing his contacts with the Pakistani Taliban before his attempt to detonate an explosives-laden vehicle in New York City's Times Square, officials said.
The evidence was part of an emphatic American warning that there would be "inevitable pressure" on the United States to take action if there was an attack traceable to Pakistan that resulted in U.S. casualties, officials familiar with the talks said.
The warning was delivered last week in a visit to Islamabad, the Pakistani capital, by White House National Security Advisor James L. Jones and CIA Director Leon E. Panetta, who said Pakistan needed to intensify its crackdown on the Pakistani Taliban, known as Tehrik-e-Taliban, or TTP, and other militant groups.
Originally, officials in Islamabad denied that the Pakistani Taliban, a militant group based in the country's tribal regions, was involved in the May 1 bombing attempt. But in the days since Jones and Panetta met with President Asif Ali Zardari and other leaders, Pakistani officials have begun to acknowledge that the group provided support to Shahzad.
The Taliban initially claimed responsibility for the attempted attack, though it later backed away from the claim and denied even knowing Shahzad.
U.S. officials have become convinced that the TTP, after primarily focusing on attacks against the Pakistani government, is increasingly seeking ways to strike U.S. targets. The group has formed closer links with Al Qaeda and has seemed to adopt the terrorist network's goal of striking the United States on its own territory.
"We have been lucky in the past, but our luck will run out and in the future, we are likely to face successful attacks," said a senior U.S. intelligence official, who, like several others, was not authorized to comment publicly and spoke on condition of anonymity.
The evidence, which included photographs of militants suspected of assisting Shahzad, was shown to Zardari and Gen. Ashfaq Kayani, the army chief of staff, along with other Pakistani officials, U.S. officials said.
Jones and Panetta were attempting to convince the Pakistanis that the U.S. had hard evidence that Shahzad had received support from the Pakistani Taliban, the officials said.
The chart, which was assembled by U.S. intelligence agencies, "showed who all he had contacts with," one official said, and drew "clear links between Faisal Shahzad and the TTP leaders in Pakistan."
Jones and Panetta did not spell out action the United States might take, the official said. The delegation did not rule out military action, for example, but it didn't talk about it specifically, he said.
Whether the U.S. would respond militarily or with lesser steps would depend on the circumstances of an attack and the strength of the evidence implicating militants in Pakistan, several officials said.
The White House originally considered warning Pakistan about the consequences of another attack in a confidential letter from President Obama to Zardari, but it decided to dispatch Jones and Panetta to deliver the message in person.
In addition to that visit, Secretary of State Hillary Rodham Clinton warned publicly in the days after the Times Square attempt that Pakistan faced "very severe consequences" in the event of another plot originating in Pakistan. Her comment provoked a strong backlash in Pakistan.
The Obama administration has been pleased with recent Pakistani military offensives undertaken in the tribal areas. U.S. officials want Islamabad to do more, especially in North Waziristan, but they acknowledge that Pakistan's military already is stretched.
A U.S. campaign of attacks launched by unmanned aircraft in Pakistan's tribal belt has been intensified since Obama took office. Pakistan is highly resistant to more than a token U.S. military presence on its territory, and American officials say there are few additional options for unilateral action against militant groups in Pakistan.
But if a terrorist attack launched from the Pakistani tribal belt did result in U.S. casualties, the pressure on the White House to act could be overwhelming, said Bruce Riedel, a former CIA official and a terrorism expert at the Brookings Institution.
"Professions by the Pakistanis that they are trying hard won't cut it anymore," Riedel said.