Squatting on the floor, a brown shawl draped over his shoulders, the Taliban commander and his bodyguard swiped on their phones through attack footage edited to look like video games, with computerised crosshairs hovering over targets. “Allahu Akbar,” they said every time a government Humvee hit a landmine.

Mullah Abdul Saeed, who met the Guardian in the barren backcountry of Logar province where he leads 150 Taliban militants, has fought foreign soldiers and their Afghan allies since the US-led coalition invaded Afghanistan when he was 14. The Taliban now controls its largest territory since being forced from power, and seems to have no shortage of recruits.

By prolonging and expanding its military presence in Afghanistan, the US aims to coerce the Taliban to lay down arms, but risks hardening insurgents who have always demanded withdrawal of foreign troops before peace talks.

In interviews with rank-and-file Taliban fighters in Logar and another of Afghanistan’s embattled provinces, Wardak, the Guardian found a fragmented but resilient movement, united in resistance against foreign intervention.

Referring to Barack Obama’s surge, Saeed said: “150,000 Americans couldn’t beat us.” And an extra 4,000 US soldiers, as Donald Trump will deploy, “will not change the morale of our mujahideen,” he said. “The Americans were walking in our villages, and we pushed them out.” For the Taliban to consider peace, he said, “foreigners must leave, and the constitution must be changed to sharia.”

The war America can't win: how the Taliban are regaining control in Afghanistan Read more

Active Taliban footsoldiers rarely agree to meet western reporters. Men such as Saeed, who spoke without leadership permission, provide valuable insight into a movement that after 16 years in armed opposition remains largely an enigma.

Arriving on a motorbike kicking up dust, Saeed and his Kalashnikov-carrying bodyguard, Yamin, were aloof at first but warmed as the conversation evolved. Saeed said that as the war has changed, the Taliban have adjusted, too. US soldiers now predominantly train Afghans, and have ramped up airstrikes.

“It’s true, it has become harder to fight the Americans. But we use suicide bombers, and we will use more of them,” Saeed said. “If the US changes its tactics of fighting, so do we.” That change has meant ever-fiercer attacks, with large truck bombs in populated areas and audacious assaults on military bases.

In April, Taliban fighters in army uniforms stormed a northern army academy and killed at least 150 soldiers in the biggest assault on the army of the entire war. This month, suicide bombers wiped out a whole army unit, ramming two Humvees packed with explosives into a base in Kandahar.

As Saeed spoke, three young boys from the civilian family at the house where the interview took place brought tea. They giggled as they listened in on the fighters’ radio. Saeed spoke with a calm, professorial demeanour but his words brimmed with the anger of a man who has spent his adult life fighting a generation-long war, and lost 12 family members doing it.

Pressed on the record-high number of civilian deaths in the war, he said the Taliban “make mistakes” and try to avoid harming civilians, but added: “If there is an infidel in a flock of sheep, you are permitted to attack that flock of sheep.”

Facebook Twitter Pinterest ‘We use suicide bombers, and we will use more of them,’ said Mullah Abdul Saeed. Photograph: Andrew Quilty/The Guardian

The Taliban was always outnumbered and technologically outmatched by its foreign adversaries, but is arguably at its strongest since 2001, threatening several provincial capitals. The movement, though, is divided, with some lower-ranking commanders backing rivals of the current chief, Mawlawi Haibatullah, or more radical outfits such as Islamic State. But rifts have not stopped the group from advancing.

Saeed claimed: “10-15 people join the mujahideen [in Logar] every day, sometimes also policemen,” adding that mistreatment by government and foreign forces helps recruitment.

“Many Taliban become suicide bombers after prison. Why?” he asked, describing how prison guards torture detainees by applying air pressure, beatings or electric shock to their genitals. After a detainee is released, he said, the shame is too much to bear. Such claims of government torture have been documented by the UN.

While few in the international community think the war can be won militarily, the US shows little intention of reviving the dormant peace process. “We are not nation-building again. We are killing terrorists,” Trump said when announcing his south Asia strategy. “In the end we will win.” Crucially, Trump has not established criteria for when US troops will be pulled home.

In a separate interview in the beleaguered Wardak province, Omari, 23, who has six years’ frontline experience, told the Guardian he had considered leaving the insurgency and taking his family to Kabul. “But if the Americans come back to Wardak, I will fight them,” he said. Omari was less cavalier than Saeed about civilian casualties, which he said damaged the Taliban’s standing with ordinary Afghans, who have become more reluctant to shelter them.

Yet, the two militants did agree on one thing: American soft power is as dangerous as uniformed soldiers, especially as US troops have dwindled in numbers. That belief materialised last year when militants, in a stunningly grisly attack, stormed the American University in Kabul, killing 16 students and staff members. In the capital, many regard the university as one of the pinnacles of post-Taliban Afghanistan.

Though no group claimed responsibility for the attack, Saeed and Omari agreed the university posed a threat. “We should kill those teachers who change the minds of society,” Saeed said.

Currently, the Taliban seem capable of upholding a slow-burning war, with the help of outside benefactors. After recent US pressure on Pakistan to crack down on militant sanctuaries, some Taliban fighters consider opting for another regional neighbour, Omari said: “Many Taliban want to leave Pakistan for Iran. They don’t trust Pakistan anymore.”

Pakistan denies harbouring militants, but Saeed admitted receiving assistance from Pakistan, though he denied being under anyone’s thumb. “Having relations is one thing, taking orders is something else,” he said. “Every party, if they want to be stronger, need to talk to other countries. We should talk to Iran, and we should talk to Pakistan. Just like the Afghan government goes to India and China.”

Names of sources have been changed to protect their identities.