Rod Nordland reports: Every bomb, they say, has a return address.

When car bombs blew up in West Beirut, or explosions cut down worshipers in Sadr City mosques, survivors generally knew who was to blame, and more or less why — even when no one claimed responsibility.

So, too, with the suicide car bomb that on Saturday delivered the worst blow that NATO forces have suffered yet in Kabul, smashing into an armored bus full of troops and killing 13 foreigners, most of them Americans, and at least 4 Afghans.

The Taliban immediately claimed responsibility, but Afghan and American officials suspect that, more specifically, it was the fearsome Haqqani faction, whose fighters have proved better trained and organized than many Taliban, and which in recent months especially has focused its attacks on military targets rather than civilian ones.

The message the Haqqanis are sending — to the world and, especially, to the Afghan public — is that they are willing and able to kill foreign troops. And with the Haqqani bombs comes a particularly troublesome return address: Pakistan, where the group is based.

One Western diplomat, speaking on the condition of anonymity under diplomatic ground rules, said it was clear that if the Haqqanis were behind the attack, the militants were reacting to Secretary of State Hillary Rodham Clinton’s recent trip to Pakistan. During the visit, she again demanded that the government do something about the Haqqanis, whose bases are in the Pakistani territory of North Waziristan.

“No one goes to this much trouble if they don’t think you’ll get the message,” the diplomat said.

An Afghan political analyst, Haroun Mir, agreed. “These are planned attacks in response to the pressure from the United States on Pakistan against the Haqqani network,” Mr. Mir said. Beyond that, he added, “the Pakistanis are sending another message, too: They are not willing to abandon their support of the Taliban.”

The New York Times also reports: Just a month after accusing Pakistan’s spy agency of secretly supporting the Haqqani terrorist network, which has mounted attacks on Americans, the Obama administration is now relying on the same intelligence service to help organize and kick-start reconciliation talks aimed at ending the war in Afghanistan.

The revamped approach, which Secretary of State Hillary Rodham Clinton called “Fight, Talk, Build” during a high-level United States delegation’s visit to Kabul and Islamabad this month, combines continued American air and ground strikes against the Haqqani network and the Taliban with an insistence that Pakistan’s Inter-Services Intelligence agency get them to the negotiating table.

But some elements of the ISI see little advantage in forcing those negotiations, because they see the insurgents as perhaps their best bet for maintaining influence in Afghanistan as the United States reduces its presence there.

The strategy is emerging amid an increase in the pace of attacks against Americans in Kabul, including a suicide attack on Saturday that killed as many as 10 Americans and in which the Haqqanis are suspected . It is the latest effort at brokering a deal with militants before the last of 33,000 American “surge” troops prepare to pull out of Afghanistan by September, and comes as early hopes in the White House about having the outlines of a deal in time for a multinational conference Dec. 5 in Bonn, Germany, have been all but abandoned.

But even inside the Obama administration, the new initiative has been met with deep skepticism, in part because the Pakistani government has developed its own strategy, one at odds with Mrs. Clinton’s on several key points. One senior American official summarized the Pakistani position as “Cease-fire, Talk, Wait for the Americans to Leave.”

In short, the United States is in the position of having to rely heavily on the ISI to help broker a deal with the same group of militants that leaders in Washington say the spy agency is financing and supporting.

“The Pakistanis see the contradictions in the American approach,” said Shamila N. Chaudhary, a former top Obama White House aide on Pakistan and Afghanistan. “The big question for the administration is, What can the Pakistanis actually deliver? Pakistan is holding its cards very closely.”