A senior leader of the feared Haqqani militant network, Nasiruddin Haqqani, was shot dead on the outskirts of Islamabad on Nov 11, 2013, by a man riding a motorcycle, was gunned down outside a bread store in a new blow to the close-knit cluster of militant groups that shelter in northwestern Pakistan.

Intelligence officials believe that he was a chief fund-raiser for the Haqqani network, one of the most lethal elements of the insurgency in Afghanistan, and he was designated as a “global terrorist” by the United States in 2010. Two commanders for the group confirmed his death on Nov 11.

“We have received his body, and the funeral has taken place,” said one commander, Gul Hassan, who spoke by phone from North Waziristan, the main hub of the Haqqani group in Pakistan. “The mujahedeen are in shock.”

The killing added to an impression of increased turbulence for the militant groups harbored in Pakistan’s tribal belt, including Al Qaeda, the Pakistani Taliban and the Haqqani network. Over just two months, one major leader has been arrested, two have been killed in a drone strike, and now a major financier — Mr. Haqqani — has died.

The link, if any, between those events remains hidden in the miasma of tribal politics, skulduggery and treachery that has for centuries haunted the rugged frontier between Pakistan and Afghanistan. But many are taking the violence as a portent of increased upheaval as rival intelligence services and militant groups vie for power and influence ahead of the withdrawal of American combat troops from the region in 2014.

The first major shot came when American forces detained Latif Mehsud, a senior commander for the Pakistani Taliban, inside Afghanistan. Weeks later, on Nov. 1, a CIA drone strike killed the Pakistani Taliban’s leader, Hakimullah Mehsud, and a top deputy. Now, Mr. Haqqani, a looming figure in a militant network closely allied with the Taliban and Al Qaeda, is dead.

There was no claim of responsibility for Mr. Haqqani’s death, although conflicting views about the identity of his killers abounded. Afghan intelligence officials quickly blamed an internal Haqqani family dispute. But among Pakistani spymasters, speculation was rife that their Afghan counterparts had ordered the hit, possibly through a network of Afghan operatives in Pakistan.

In any case, the fact that he was killed on the very edge of Islamabad, is likely to discomfit the Pakistani government and military, which have long faced accusations that they allow the Haqqanis and other militant groups nearly complete freedom of movement within the country.

Another Haqqani network commander claimed that militants had mourned Mr. Haqqani at a prayer service right under the nose of the Pakistani military, at a secret spot in the garrison city of Rawalpindi, near Islamabad. The commander said that Mr. Haqqani’s body was then sent back to the tribal belt for burial.

American and Afghan officials have for years accused Pakistani intelligence officials of aiding, or at least turning a blind eye to, the Haqqani network as part of a strategy to maintain influence in Afghanistan, and to attack Indian diplomatic sites in the country.

Pakistani officials deny any collusion with the group but admit that they keep in contact with its commanders as part of intelligence operations. And they make little secret of the fact that the Haqqanis were their trump card in efforts to draw the Afghan Taliban, which are linked to the Haqqani network, into peace talks.

Nasiruddin Haqqani, who shuttled between the tribal belt and the Islamabad area, was sometimes described as one of the group’s liaisons with the ISI.

But the recent round of killings and arrests, on both sides of the border, seems to suggest that some players are more interested in shooting than in negotiating for peace, at least for now.

American interest in the Haqqani network stems from its record of well-organized attacks against high-profile targets in Afghanistan’s major cities. The group pledges allegiance to the Afghan Taliban but operates with a high degree of autonomy, and over the years it has launched coordinated assaults on government ministries, five-star hotels and the United States Embassy in central Kabul, on American bases near the border with Pakistan, and on Indian diplomatic facilities across the country.

Fund-raising is also crucial to the group’s success, thanks to its involvement in drug smuggling, kidnapping and gun running, as well as decades-old links to rich jihadi donors in the Persian Gulf states, such as Saudi Arabia.

American, German and British officials saw Nasiruddin Haqqani, whose mother is Arab and who spoke Arabic, as the crucial link between the network and the legitimate businesses in the Persian Gulf area that it profits from.

The Haqqani network began as a mujahedeen group fighting the Soviet occupation of Afghanistan in the 1980s. Back then, its leader, Mr. Haqqani’s father, Jalaluddin, was a towering figure of the resistance, and he was both a cherished ally of the United States and a hero figure in the Persian Gulf states, where he led fund-raising tours of mosques.

In recent years, as the group turned its sights toward driving the American military out of the country, command of the group passed to his son Sirajuddin. Most of the group’s leadership moved to the Pakistani tribal belt, nominally out of reach of the American military offensives targeting the network next door in eastern Afghanistan.

But the CIA drone program continued to take a toll.

Another Haqqani son, Badruddin, was killed in a drone strike in North Waziristan in August 2012.

Nasiruddin Haqqani was buried in the same graveyard as his brother, in Danday Darpa Khel — the village where Hakimullah Mehsud, the leader of the Pakistani Taliban, was killed in a drone strike.

Some Afghan officials said they thought it was family politics, in the end, that brought Nasiruddin Haqqani down. A tribal leader in the eastern Afghan province of Khost, the main stronghold of the Haqqani family’s tribe, said that Mr. Haqqani had a long-running financial dispute with a cousin, Ishaq, whom he had accused of working with Afghan intelligence officials.

The Haqqani network has reportedly faced internal strain, with accounts of discontent and even resentment within its tribal support base in eastern Afghanistan’s rugged mountains.