U.S. Military Calls ISIS in Afghanistan a Threat to the West. Intelligence Officials Disagree.

WASHINGTON — Senior United States military and intelligence officials are sharply divided over how much of a threat the Islamic State in Afghanistan poses to the West, a critical point in the Trump administration’s debate over whether American troops stay or withdraw after nearly 18 years of war.

American military commanders in Afghanistan have described the Islamic State affiliate there as a growing problem that is capable of inspiring and directing attacks in western countries, including the United States.

But intelligence officials in Washington disagree, arguing the group is mostly incapable of exporting terrorism worldwide. The officials believe that the Islamic State in Afghanistan, known as Islamic State Khorasan, remains a regional problem and is more of a threat to the Taliban than to the West.

Differences between the American military and Washington’s intelligence community over Afghanistan are almost as enduring as the war itself. The Pentagon and spy agencies have long differed over the strength of the Taliban and the effectiveness of the military’s campaign in Afghanistan.

Whether to keep counterterrorism forces in Afghanistan is at the heart of the Trump administration’s internal debate over the future of the war.

Ten current and former American and European officials who are familiar with the military and intelligence assessments of the strength of Islamic State in Afghanistan provided details of the debate to The New York Times. The officials spoke on the condition of anonymity to candidly discuss the issue and confidential assessments of the terrorism threat.

A State Department envoy is leading negotiations for a peace deal that would give the Taliban political power in Afghanistan and withdraw international troops. For months, the Trump administration has been drafting plans to cut the 14,000 American forces who are currently there by half. On Monday, Secretary of State Mike Pompeo said Mr. Trump had ordered a reduction in the number of troops in Afghanistan before the 2020 presidential election, but he did not specify a number.

“That’s my directive from the president of the United States,” Mr. Pompeo told the Economic Club of Washington. “He’s been unambiguous: End the endless wars. Draw down. Reduce. It won’t just be us.”

Yet at the same time, current and former officials, including the retired Army generals Jack Keane and David H. Petraeus, are lobbying the Trump administration to maintain several thousand Special Operations forces in Afghanistan. Doing so, they argue, will keep terrorist groups from returning and help prevent the collapse of the Afghan government and its security forces.

“U.S. troops in Afghanistan have prevented another catastrophic attack on our homeland for 18 years,” General Keane said in an interview. “Expecting the Taliban to provide that guarantee in the future by withdrawing all U.S. troops makes no sense.”

In Afghanistan, the threat of Islamic State is not a point of debate.

Brig. Gen. Ahmad Aziz, the commander of an Afghan Special Police Unit, said that Islamic State attacks in Kabul, the capital, are becoming more advanced and that the group is growing.

During a May tour of the communications ministry in Kabul, General Aziz pointed out a neat, circular hole cut at a weak point between two walls. A month earlier, he said, Islamic State gunmen had slipped through the hole and into the building to kill at least seven people.

“Their breach points are evolving,” General Aziz said, “and they’re picking targets that are more difficult for us to get to.”

Military and intelligence officials do agree that the Islamic State, unlike the Taliban or other terrorist groups in Afghanistan, has focused on so-called soft targets such as civilian centers in Kabul and the city of Jalalabad.

But on the key question — whether the Islamic State can reach beyond the borders of Afghanistan and strike the West — the American military in Afghanistan and intelligence agencies in Washington diverge.

One senior intelligence official said the Islamic State’s Afghanistan branch lacks the organizational sophistication of the core group in Syria and Iraq, which had a bureaucracy dedicated to planning attacks in Europe and cultivating operatives overseas.

Ambassador Nathan A. Sales, the State Department’s counterterror coordinator, called the Islamic State Khorasan “a major problem in the region.” And, he added, it poses a threat to the United States.

“What we have to do is make sure that ISIS-Khorasan, which has committed a number of attacks in the region, is not able to engage in external operations,” Mr. Sales told reporters at the State Department on Thursday.

Some analysts said it was dangerous to suggest that the Islamic State in Afghanistan did not have the capability to threaten the West.

“I would never rule out any of these jihadis ever threatening the West, because their ideology is inherently anti-America,” said Thomas Joscelyn, a senior fellow at the Foundation for Defense of Democracies in Washington.

But whether the American military should remain in Afghanistan, he said, should not hinge just on the threat from Islamic State or other extremists. “The war has been stagnant and poorly managed for so long,” Mr. Joscelyn said, “that it is hard to argue for the status quo.”

The Islamic State in Afghanistan surfaced in 2015 and was quickly dismissed by Pentagon officials merely as a breakaway group from the Taliban in Pakistan, but one with little ability to expand given the pervasiveness of other hard-liners.

Four years later, the Islamic State Khorasan is made up of roughly 3,000 fighters and is well resourced, funded and entrenched in the rural areas of eastern Afghanistan.

A United Nations report released this week concluded that the Islamic State Khorasan was responsible for 423 of the 3,812 civilians — about 11 percent — who were killed or wounded in Afghanistan during the first six months of 2019.

Intelligence officials in Washington said the territory controlled by the Islamic State in Afghanistan was not of strategic importance — much like Pakistan’s lawless frontier. Neither government officials in Kabul nor foreign forces have ever truly controlled the rural mountain ranges that run along Afghanistan’s eastern border.

When the Islamic State grabbed territory in Jowzjan Province last year, American officials and Taliban leaders alike were concerned. But officials said the Taliban, following a concerted bombing campaign by American aircraft, pushed out the Islamic State, which since has been unable to capture land outside the provinces of Nangarhar and Kunar.

American military officials in Kabul said broad assessments from Washington often belie evidence that United States troops find on the battlefield, such as information gleaned on raids and from materials like cellphones. That intelligence, the officials said, has portrayed an expanding Islamic State recruiting network and an extremist influence that extends well outside the country.

In one example, a senior intelligence official said, evidence compiled from Afghanistan showed that an Islamic State leader in Nangarhar Province helped inspire and direct an April 7, 2017, terrorist attack that killed five people and wounded at least 12 in Stockholm.

The Islamic State remains a threat to American forces in Afghanistan. At least a half-dozen American troops have been killed fighting the group since 2015, and a C.I.A. contractor lost a leg in an Islamic State attack last fall.

But the size of the group remains a sticking point between the military and intelligence agencies.

Military officials at the United States Central Command, which oversees the wars in Afghanistan and Iraq, have routinely doubled the estimated number of fighters that intelligence officials had separately predicted would be present in a given village or area, according to two American officials.

In part, the spy agencies’ assessments are the result of their reliance on technical intelligence collection, like drones sweeping over training camps and electronic eavesdropping on cellphones and other communications.

The National Security Agency can count cellphone signals from known insurgents or terrorists. But, officials said, many fighters do not carry cellphones, and those who do are increasingly encrypting their messages. An N.S.A. spokesman declined to comment.

The Islamic State, in both the Middle East and Afghanistan, has proved adept at swelling its numbers quickly. It has armed civilians and pushed them into battle, conscripted others into its ranks and converted administrative workers into fighters.

The undercounting of fighters has proved most dangerous ahead of raids on Islamic State safe houses, where Special Operation forces and Afghan commandos have found far more militants than intelligence agencies predicted.

Some military officials believe the undercounting has caused the intelligence agencies to underestimate the threat of the Islamic State.

The American military’s reconsideration of the threat and expansion of the Islamic State is partly a byproduct of an intelligence failure in 2015, when United States forces were startled to find an expansive Qaeda training camp in rural Kandahar Province.

The discovery alarmed military officials, who long thought the terrorist group had been reduced to a few dozen stragglers spread around the country, one former White House official said.