Afghan policemen stand guard at the site of a suicide attack in front of the Indian Embassy in Kabul in 2008. (Sardar Ahmad/Agence France-Presse via Getty Images)

— When a fake sewage tanker truck carrying 3,000 pounds of explosives managed to reach a high-security district of Kabul on May 31, then detonated in an explosion that left 150 people dead and 400 wounded, no insurgent or terrorist group asserted responsibility. But immediately, the rumors began to spread.

The Haqqanis. It had to be the Haqqani network, people said. No one else could have pulled off such a precise and spectacular crime. The Afghan intelligence police soon publicly accused the group, too, adding that it had gotten help from Pakistan’s spy agency. Seven weeks later, the bombing remains unclaimed, and the Afghan capital is still reeling from it.

By rights, the Haqqanis should be barely standing. For years, this clan-based Taliban offshoot has been a high-priority target for Afghan forces and their U.S.-led allies. The group’s charismatic founder, Jalaluddin Haqqani, is believed to have died of illness, and most of his sons and senior commanders have been killed or imprisoned. Pakistan, which once allowed the Haqqanis to rule their own ministate in the border badlands, now claims to have driven them out.

So why does the name “Haq­qani network” still evoke such dread? Why is this group of a few thousand fighters still center stage in a grinding 16-year war, and why have their elusive whereabouts become Exhibit A among those who say that the Trump administration must punish Pakistan, a longtime security and military ally, for harboring terrorists?

The answers to the Haqqanis’ survival have much to do with qualities that Jalaluddin Haq­qani, a former Taliban minister and friend of Osama bin Laden, cultivated and passed on to his surviving son and successor, Sira­juddin. These include kinship bonds and unwavering religious ideology, strong discipline and careful planning, and an enduring ability to attract supporters, whether young suicide-bomber trainees or generous Middle Eastern backers.

Jalaluddin Haqqani, founder of the Haqqani network, speaks during an interview in Miram Shah, Pakistan, in 1998. (Mohammed Riaz/Associated Press)

This mix of assets helped the Haqqanis carry out a long list of deadly and high-profile attacks in Kabul during the past decade, including an assault on the Indian Embassy and another on the fortresslike Serena hotel. The group, always close to al-Qaeda, is widely said to have introduced suicide bombings to the Afghan conflict, and the one on May 31 was especially horrific.

[Pakistan pivots to China amid fresh concerns over U.S. ties with India]

U.S. officials have accused Pakistan of providing sanctuary to the Haqqanis — keeping them as a proxy force while purporting to want peace in the region. The issue has sharpened as the Trump administration grapples with what policies to take in the conflicted region and as U.S. military officials have argued for a stepped-up military presence.

The U.S. commander in Afghanistan, Gen. John W. Nicholson, told a Senate committee in February that the Taliban and the Haqqanis in particular are “the greatest threats to security in Afghanistan” and that their leaders “enjoy freedom of action within Pakistan safe havens.” The Haqqani network was designated a foreign terrorist organization by the Obama administration in 2012.

Pakistan has repeatedly denied that it harbors or assists the Haqqanis, saying they were driven out of its border tribal region of North Waziristan, along with other insurgent groups, in a counterterrorism campaign by the Pakistani army in 2014-2015.

“The Haqqani network has no presence in Pakistan. It is being operated from Afghanistan,” Pakistan’s Foreign Ministry spokesman said last month. He said that Afghans and their foreign allies are blaming Pakistan for their own failures. “The terrorists are on the run, and they have settled in the ungoverned spaces in Afghanistan,” he said.

An Afghan Taliban spokesman, Zabiullah Mujahid, said in a telephone interview that while some families of Taliban commanders may still live in Pakistan as part of the Afghan refugee community, there is “no truth to the allegations that any Taliban, including the Haqqani network, are being supported by Pakistan or living freely there.”

In early June, the usually elusive Sirajuddin Haqqani posted a long audio message in Afghan Pashto on the Taliban WhatsApp account. In it, he condemned the May 31 bombing and said his fighters had been ordered to avoid attacks in public places where “innocent civilians” were likely to be harmed.

Yet he accused Afghanistan’s foreign allies of trying to “occupy our land and take away the Islamic system from Afghanistan. How could we close our eyes?” he said. “Our aim is to free Afghanistan from their control and influence and enforce the Islamic system. We have lost thousands of lives, made thousands of widows and orphans in this jihad. So we have to take it to its logical ends.”

Haqqani, believed to be in his 40s, has kept a low profile since succeeding his father as commander of the Taliban faction. With a $5 million U.S. bounty for his capture and a history of drone strikes killing his associates, he is said to be permanently on the move. Local supporters in Pakistan said they have not seen him in two years.

[Pakistan, accused of terrorist infiltration, starts to fence its border with Afghanistan]

But southeastern Afghanistan, especially Khost province along the Pakistan border, remains the Haqqanis’ wartime comfort zone. Sirajuddin Haqqani commands a guerrilla force of at least 5,000 motivated fighters who address him as “khalifa,” or Islamic spiritual leader. One civilian supporter said he had also met Afghan government soldiers and police who helped the Haqqanis carry out attacks in “highly sensitive zones.”

A spokesman for the Haqqanis in Pakistan declined to answer questions by phone. Supporters and analysts said that the group maintains ties with Pakistan’s intelligence service from their anti-Soviet collaboration but that it no longer enjoys free rein, largely due to U.S. pressure.

“Pakistan is no longer a safe place for the Afghan Taliban,” said Muhammad Israr Madani, an Islamic cleric and researcher in Pakistan.

In the past, he said, “some got national identity cards, but now the government has blocked them. I can’t deny the presence of Afghan Taliban and Haqqanis still living in Pakistan, but now it is very difficult for them to live here in peace.”

Maulana Samiul Haq, a cleric whose seminary near Peshawar has produced many Afghan Taliban fighters, said that the Haqqani network is still “the most active and dreaded” Taliban entity but that Pakistan’s influence on the fighters has “weakened” under U.S. pressure. Once, he said, top military and spy officials “welcomed them, but now they avoid meeting them.”

Yet despite Pakistan’s efforts to distance itself from the Haq­qanis, some of their supporters are convinced this is only a tactical retreat in Pakistan’s long-term campaign to dominate and weaken Afghanistan. “Khalifa is the last hope, and Pakistan will not want to lose him,” said a tribal cleric who is close to the Haq­qanis.

From their murky border hideouts and camps, the Haqqanis are also known for kidnapping foreigners as hostages. A Canadian American family has been in their custody since 2012, when they were seized on a hiking trip. In a video released by the group in December, the American mother, Caitlin Coleman, 31, pleaded with then-President-elect Donald Trump to save them from “our Kafkaesque nightmare.”

The group has demanded that one of Sirajuddin Haqqani’s brothers, who is in prison in Kabul under a death sentence, be spared. If he is executed, it has threatened to kill the family.

Constable reported from Kabul.

Read more:

In Pakistan, scorching Ramadan month highlights chronic water, power shortages

On July 4 visit to Kabul, GOP senators say U.S. needs to win in Afghanistan

Pakistan’s prime minister, having survived Supreme Court corruption ruling, now faces pressure

Today’s coverage from Post correspondents around the world

Like Washington Post World on Facebook and stay updated on foreign news