This article was written by Mark Mazzetti, Scott Shane and Alissa J. Rubin.

WASHINGTON — They are the Sopranos of the Afghanistan war, a ruthless crime family that built an empire out of kidnapping, extortion, smuggling, even trucking. They have trafficked in precious gems, stolen lumber and demanded protection money from businesses building roads and schools with American reconstruction funds.

They safeguard their mountainous turf by planting deadly roadside bombs and shelling remote American military bases. And they are accused by American officials of being guns for hire: a proxy force used by the Pakistani intelligence service to carry out grisly, high-profile attacks in Kabul and throughout the country.

Today, American intelligence and military officials call the crime clan known as the Haqqani network — led by a wizened militant named Jalaluddin Haqqani who has allied himself over the years with the C.I.A., Saudi Arabia’s spy service and Osama bin Laden — the most deadly insurgent group in Afghanistan. In the latest of a series of ever bolder strikes, the group staged a daylong assault on the United States Embassy in Kabul, an attack Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, charged Thursday was aided by Pakistan’s military spy agency, the Directorate for Inter-Services Intelligence, or ISI. According to two American officials, cellphones used by the attackers made calls to suspected ISI operatives before the attack, although top Pakistani officials deny their government played any role.

But even as the Americans pledge revenge against the Haqqanis, and even amid a new debate in the Obama administration about how to blunt the group’s power, there is a growing belief that it could be too late. To many frustrated officials, they represent a missed opportunity with haunting consequences. Responsible for hundreds of American deaths, the Haqqanis probably will outlast the United States troops in Afghanistan and command large swaths of territory there once the shooting stops.