U.S. officials this summer secretly met with leaders of the deadly Haqqani network, the Afghan militant group closely tied to al Qaeda, in an effort to draw them into talks on winding down the war.

Washington has publicly scorned the group, which is blamed with bringing a new level of violence to the Afghan insurgency and is at the center of the deteriorating U.S. relationship with Pakistan.

Pakistan and U.S. officials said the push to draw the Haqqanis into talks has yielded little. The U.S. says Haqqani fighters were responsible for a 20-hour assault last month on the U.S. Embassy and the nearby North Atlantic Treaty Organization headquarters in Kabul.

The Haqqani network is regarded by American officials as an irredeemably violent militant and criminal network tied to al Qaeda and supported by the Pakistani intelligence service. Haqqani fighters are regularly targeted by U.S. drone strikes in Pakistan. U.S. officials have long said they were beyond reconciliation.

But the behind-the-scenes American effort reflects the growing realization that a military campaign alone won't bring the Haqqanis to heel—and that compromises are needed to wind down U.S. involvement in Afghanistan.

U.S. officials had already reached that conclusion about the Taliban—saying that losses on the battlefield would drive Taliban leaders to the negotiating table.

"We've got no illusions about what the Haqqanis ultimately are," said a senior U.S. official said. But the "war is going to end with a deal. That's what we're trying to make inevitable. The more parties involved in talking, that's probably going to make for a better deal."

The official declined to discuss the talks with the Haqqanis, describing them as "early and not very well defined."

That also describes the wider peace effort, which has moved in fits and starts over the past two years, making little overall progress. Afghan President Hamid Karzai has given up on negotiations with the Taliban, Afghan officials said Sunday, after the assassination of his top peace envoy, former President Burhanuddin Rabbani.

The senior U.S. official said there had been at least one meeting over the summer between U.S. officials and Haqqani representatives. The meeting was set up by Pakistan's Inter-Services Intelligence spy agency, a fact that the Americans said confirmed thier suspicions of Pakistani ties to the Haqqanis.

The meeting took place as the Haqqanis were stepping up attacks in and around Kabul, but before their most high-profile strike to date, the assault on the U.S. Embassy, which began on Sept. 13. The assault made the effort to talk to the Haqqanis more difficult, but the effort to get a peace process going hasn't been abandoned, officials said.

The State Department wouldn't comment directly on outreach to the Haqqanis. Spokesman Mark Toner, citing previous comments by Secretary of State Hillary Clinton, said: "We have a broad range of contacts across Afghanistan and the region…these contacts are preliminary in nature."

A Pakistani official said Islamabad began facilitating contacts with the Haqqanis late last year and set up the meeting this summer in a Persian Gulf country. The Afghan government didn't take part.

The U.S. wouldn't identify the participants; the Pakistani official said the insurgents were represented by one of the brothers of the main leader of the network, Sirajuddin Haqqani.

Mr. Haqqani told the BBC in an interview published on Monday that "not only Pakistan, but other Islamic countries, and other non-Islamic countries, including America, contacted us and they are still doing so."

Mr. Haqqani said the U.S. asked him to break with Taliban leader Mullah Omar and join Mr. Karzai's government, but the overtures were rebuffed, according to the report.

The Haqqanis are one of the most potent forces in the Afghan war. One U.S. defense official called them "world-class fighters, whether we like it or not."

The U.S. diplomacy diverges from the drone strikes and special-forces raids the Americans have used against the Haqqanis for much of the past three years.

U.S. officials have berated Pakistan for not attacking the faction's sanctuaries in the tribal areas on the Afghan border. Pakistan argues it lacks the resources to do so.

Pakistan for years denied U.S. accusations it aids or abets the Haqqanis, and the increasingly public dispute is now straining ties, with U.S. lawmakers threatening to cut aid and military officials in both countries pointing fingers.

The American outreach is the latest chapter in a relationship between Washington and the Haqqanis that stretches back to the Afghan Mujahedeen's fight against the 1979 Soviet invasion of their country.

The network's founder, Jalaluddin Haqqani, was one of the main mujahedeen commanders backed by the U.S. and Pakistan.

He went on to join the Taliban government that ruled Afghanistan from the mid-1990s until the 2001 U.S.-led invasion. He then took refuge in Pakistan's tribal areas and, after an aborted American attempt to lure him to their side, took up arms against his old backers.

Officials are now trying to discern just what shape stalled peace efforts will take, the senior U.S. official said.

Options include talks between Afghans and the Taliban, with the U.S. observing; Pakistan playing a direct role; or the Haqqanis having a seat separate from the Taliban. "Anyone who tells you they know what shape the process is taking doesn't know what they're talking about," another U.S. official said.

Top Pakistani officials have alluded to the U.S. contacts with the Haqqanis in recent statements responding to American accusations they support the group.

In one tart statement last month, military chief Gen. Ashfaq Parvez Kayani said the U.S. "knows fully well which … countries are in contact with the Haqqanis. Singling out Pakistan is neither fair nor productive."

A senior Pakistani military officer said Gen. Kayani was referring to the U.S.