http://online.wsj.com/article/SB10001424052970204618704576642292289411766.html

KABUL—Secretary of State Hillary Clinton told Pakistan it should crack down on insurgents staging attacks into Afghanistan, or pay a "very big price."

Mrs. Clinton, speaking in the Afghan capital on Thursday before heading to Pakistan, voiced America's impatience with Pakistan's reluctance to take action against the Afghan Taliban and the allied Haqqani network.

U.S. Secretary of State Hillary Clinton shook hands with U.S. Ambassador to Afghanistan Ryan Crocker as Afghan chief of protocol Hamid Saddiq (2nd R) and Lt. General Curtis Scaparotti (L) looked on upon Clinton's arrival in Kabul October 19, 2011.

"We must send a clear, unequivocal message to the government and the people of Pakistan that they must be part of the solution," she said during a news conference in Kabul with Afghan President Hamid Karzai. "And that means ridding their country of terrorists who kill their own people and who cross the border to kill in Afghanistan."

U.S. and Afghan officials have long contended that Pakistan's powerful military spy service, the Inter-Services Intelligence Directorate, or ISI, has supported the Taliban leadership, which is based in the Pakistani city of Quetta, and the Haqqani network, which is based in the Pakistani tribal area of North Waziristan.

The Haqqanis, these officials say, are responsible for a series of recent high-profile attacks in Kabul, including an assault on the U.S. Embassy.

"We're looking to the Pakistanis to lead on this," Mrs. Clinton said after meeting with Mr. Karzai at his fortified palace. "No one should be in any way mistaken about allowing this to continue without paying a very big price."

Pakistani officials say they don't have the resources to mount a massive operation against Afghan insurgents while the Pakistani military is still fighting a separate Pakistani Taliban insurgency elsewhere in the tribal region.

India Real Time

Clinton to Push Pakistan, Again

"This needs to be fixed," a senior U.S. official said, adding that the message Mrs. Clinton would convey to Pakistan is: "You need to deal with it or we will."

Under a tacit agreement with Pakistan, the Central Intelligence Agency has been conducting drone strikes against the Haqqanis and other Afghan insurgents in North Waziristan and other Pakistani tribal areas. One of these strikes earlier this month killed a senior Haqqani official, Janbaz Zadran.

Pakistan has rejected U.S. requests to expand operations into insurgent sanctuaries near Quetta and other parts of Pakistan.

The U.S. in the past has tried to strong-arm Pakistan into action against the Haqqani network and the Quetta-based Taliban, with little success.

U.S. lawmakers are considering legislation that would tie billions of dollars in civilian and military aid to an invasion of North Waziristan. But Mrs. Clinton and other State Department officials have pushed back, arguing that cutting off aid would hurt Pakistan's ability to defeat the militants.

The debate reflects the difficulty Washington has had in pressuring its nominal ally. The U.S. relies on Pakistan to act as a conduit for more than half of all war supplies that it ships to Afghanistan. Pakistan also is a nuclear-armed country with which the U.S. wants to remain on speaking terms.

Yet Pakistan sees longer-term interests in Afghanistan beyond the U.S. presence. Most foreign troops are slated to leave by late 2014, and many Pakistani military leaders expect the Taliban and the Haqqanis will emerge as a major power after that—making it necessary for Pakistan to be able to work with the insurgents.

Mrs. Clinton arrived on Thursday night in Pakistan, where she was to be joined by Central Intelligence Agency director David Petraeus, who until recently commanded coalition troops in Afghanistan, and the new Chairman of the U.S. Joint Chiefs of Staff, Gen. Martin Dempsey.

The two senior national security officials have been sent to convey a "unified U.S. government message" on the importance of the relationship and the need to find areas where the U.S. and Pakistan can work together, the senior U.S. official said.

A top agenda item would be taking on the Haqqanis, the official said. Before stepping down last month, Chairman of the Joint Chiefs of Staff Adm. Mike Mullen called the Haqqanis "a veritable arm" of the ISI.

Pakistani generals don't think the U.S. will back its threats with military action inside Pakistan, said Hasan-Askari Rizvi, an independent Pakistani defense analyst. "I don't think the U.S. will commit its troops to North Waziristan at a time when it's withdrawing from Afghanistan," Mr. Rizvi said.

In Afghanistan, Mr. Karzai has adopted an increasingly tough attitude toward Pakistan after a purported Taliban peace emissary from Quetta assassinated his chief peace negotiator, former President Burhanuddin Rabbani, last month.

Following the assassination, Mr. Karzai ended efforts to reach out to the Quetta-based Taliban leadership, saying that Pakistan holds the keys to any peace settlement.

"We believe the Taliban, to a very, very great extent, to a very, very great extent are controlled by the establishments in Pakistan," Mr. Karzai said at the news conference with Mrs. Clinton.

Mrs. Clinton, who met Mr. Rabbani's son Salahuddin earlier on Thursday, voiced support for Mr. Karzai's decision, while saying that an inclusive peace deal is the only way to end the 10-year-old war.

Mrs. Clinton and her aides said the U.S. is pursuing a three-pronged "fight, talk, build" strategy that would attempt to cripple insurgents on the battlefield, convince willing militant leaders to talk, and push forward with programs to shore up the Afghan economy.

Mr. Karzai's aides, who have long pressed for more direct U.S. action on Pakistani soil, said they were heartened by Mrs. Clinton's harsh warnings to Islamabad.

"There is a common ground between the U.S. and Afghanistan with regard to the sanctuaries in Pakistan, that will have to be either confronted or dismantled with the cooperation from Pakistan," said Shaida Mohammad Abdali, Mr. Karzai's deputy national security adviser. "This was one of the most engaging, cordial and visionary conversations we have had so far over the last ten years."

—Siobhan Gorman in Washington contributed to this article.