— As Taliban fighters kill a growing number of Afghan soldiers, the country’s leaders are blaming Pakistan, an accusation that has sent the neighbors’ relations to one of the lowest points in more than a decade.

Afghan officials say their allegations stem from an influx of foreigners fighting for a resurgent Afghan Taliban, as well as a Pakistani Islamist militant group’s recent announcement that it was abandoning domestic attacks and turning its sights across the border.

Afghans have long blamed Pakistan for the violence in their country, reserving special ire for the Pakistani spy organization that they and U.S. intelligence officials say has nurtured and supported Islamist militants. But those accusations are intensifying, and they now include ­charges that Pakistan’s military and Inter-Services Intelligence agency (ISI) are recruiting, training and equipping Afghan Taliban fighters as most U.S. troops withdraw from Afghanistan this year.

Pakistani officials strongly deny the charges, accusing outgoing Afghan President Hamid Karzai of paranoia and of scapegoating them for his own government’s failures. But as Afghans at all levels of the country’s government and military assert that they are being systematically undermined by Pakistan, also a key U.S. ally, the tensions are serving as a sign of how hard it will be for U.S. forces to withdraw from the region without risking a future conflict.

“We know they have not given up their dream of controlling Afghanistan,” Mohammad Umer Daudzai, the Afghan interior minister, said of Pakistan. “They want Afghanistan to be their satellite.”

Smoke rises following clashes between Afghan security forces and the Taliban insurgents during an anti-Taliban operation in Dur Baba district near the Pakistan-Afghanistan border on September 25, 2014. (Noorullah Shirzada/AFP/Getty Images)

Since spring, more than 2,000 Afghan police officers and soldiers have been killed, twice as many fatalities as during the same period last year, officials said. The death toll can be partially linked to the drawdown of coalition forces, which has left Afghan troops more vulnerable. But Afghan officials have also issued public statements accusing Pakistan of sending army commandos, doctors and military advisers to support the Afghan Taliban.

Some of their evidence is vague — officials will say only that they believe “thousands” of foreign fighters are in Afghanistan and that they include a smattering of Uzbeks, Chechens and others. But they also cite the recent announcement by the Punjabi Taliban — a Pakistani group that has carried out scores of attacks against Pakistani security forces — that it would ally with a major Afghan militant group and redirect its fighters to Afghanistan.

Karzai’s National Security Council called that a “declaration of war” and blamed the ISI. Pakistan countered with a statement deeming the Afghan allegation “unfounded and counter-productive.”

Accusations fly

To buttress their claims, Afghan intelligence officials provided to The Washington Post video statements of men they said were Pakistanis captured on the battlefield. One says he was released from a Pakistani prison by an ISI agent in exchange for agreeing to support the Taliban in Afghanistan. Another video shows a man, who Afghan intelligence analysts said was a Pakistani intelligence officer, shouting in Punjabi — one of the most widely spoken languages in Pakistan — during a recent battle in Helmand province.

“Keep aiming, keep aiming,” the man says to fighters firing toward an apparent Afghan army outpost. “Don’t get distracted.”

Afghan officials have been known to exaggerate battlefield claims. And it is difficult to confirm the latest Afghan allegations about Pakistani links to the insurgency or verify the authenticity of the videos.

But the claims have outraged Pakistani officials. “This has no relevance to reality,” said Sartaj Aziz, Pakistani Prime Minister Nawaz Sharif’s top foreign policy adviser.

Gen. Asim Bajwa, a spokesman for the Pakistani military, said Pakistan is the one suffering from terrorist attacks planned on Afghan soil.

“We have made it very clear that Pakistan is determined to eliminate all terrorists and sanctuaries from Pakistan and is also committed to ensure that our soil is never used for any terrorist activity abroad,” Bajwa said.

But that is not the view of U.S. and Afghan officials, who for years have faulted Pakistan for not doing enough to control the flow of Islamist militants from their hideouts in Pakistan’s tribal areas into Afghanistan. U.S. intelligence officials have been particularly frustrated by Pakistan’s failure to contain the Haqqani network, which carried out some of the deadliest attacks against U.S. troops in Afghanistan.

Michael Kugelman, a senior program associate for South and Southeast Asia at the Woodrow Wilson International Center for Scholars, said he thinks that the “accusations coming from Afghanistan are grounded, at least to some degree, in truth,” given reports of increasing numbers of foreigners fighting in Afghanistan.

In June, Pakistan’s military launched a major operation to dislodge the Pakistani Taliban and other Islamist militants from North Waziristan in the northwestern part of the country. Afghan officials say that was part of a Pakistani plot to quell terrorist attacks within its own borders by pushing the problem into Afghanistan.

“They were thinking: ‘Foreigners are leaving Afghanistan. They don’t have a strong air force . . . so we will ramp up our attacks and overrun provinces,’ ” said Gen. Zahir Azimi, an Afghan army spokesman, adding that Afghan intelligence has intercepted phone conversations between militants and suspected ISI agents.

There is a long history of skepticism between the neighbors. Part of the job of Afghan military “religious affairs advisers,” for example, is to keep up morale by telling Afghan troops that Pakistan is fueling the Taliban insurgency.

“We tell them, ‘Pakistan wants a weak country to sell its good goods here, to sell them to us at high prices,’ ” said one adviser, who said he was not authorized to speak to the news media.

Afghan commanders said they have little doubt those advisers are speaking the truth, especially after this summer’s fierce fighting. With each new battle, they said, field commanders returned with stories of foreign fighters.

“Foreign fighters are commanding Afghan Taliban fighters, and the foreign fighters are well equipped,” said Lt. Col. Mohsin Sultani, a spokesman for an Afghan Army unit in southern Afghanistan.

Tensions in border areas

In perhaps the most serious diplomatic tussle between the two countries, Afghan officials also accuse Pakistan of having fired nearly 5,000 rockets into eastern Afghanistan since late spring — in a bid, they say, to depopulate border areas so militants driven from North Waziristan can establish bases in Afghanistan.

Pakistani military officials say they fire into Afghanistan only when their forces are attacked from that side of the border. One of Pakistan’s most-wanted terrorist leaders, Pakistani Taliban commander Maulana Fazlullah, is believed to live in eastern Afghanistan.

Pakistan is also in the process of digging a six-foot-deep, 100-mile-long trench in southwest Baluchistan province to keep militants and drug smugglers from crossing the border.

Zahid Hussain, an Islamabad-based defense expert, said such measures, as well as the loose affiliation between the Afghan and Pakistani Taliban, make him skeptical that Pakistani security forces would want to prop up the Afghan group.

“It’s clear any rise of the Taliban in Afghanistan would create even more problems for Pakistan, and that has basically been the general feeling here for at least two or three years,” Hussain said.

But Kugelman said that Pakistan’s “security establishment is hardly monolithic.” He said he fears some elements are working to destabilize Afghanistan to prevent its deepening ties with India, Pakistan’s longtime foe.

“Bottom line, it’s complicated,” Kugelman said. “But there is a proxy war going on there.”

Sharif Hassan contributed to this report.