The U.S. military killed Abdul Hasib, the top leader of Afghanistan’s Islamic State branch, in an airstrike targeting the jihadist group in its main stronghold in the region, located in the eastern part of the war-devastated country along the Pakistan border, officials from both countries have conceded.

“This successful joint operation is another important step in our relentless campaign to defeat ISIS-K in 2017,” the top U.S. and NATO commander in Afghanistan, Gen. John Nicholson said in a statement issued Sunday from U.S. military headquarters in Kabul.

The U.S. military has dealt a major blow to an already degraded but resilient ISIS-K in recent months.

“Afghan officials said at least 34 militants had been killed by Afghan airstrikes since Sunday but gave no figures on Afghan casualties.” reports the Washington Post (WaPo). The role of U.S.-led coalition forces in the latest phase of the offensive was not immediately clear.

The U.S. troops, supported by Afghan forces, have dramatically reduced the ISIS-K military footprint from a peak of as many as 3,000 to 600 now, WaPo learned from Navy Capt. William Salvin, as spokesman for American troops in Afghanistan.

Islamic State jihadists have also suffered fatalities from battles their rival Taliban fighters who are fighting against the Iraq-Syria-based group for territory, jihadists, resources, and influence over the population.

“ISIS is believed to maintain links with the main Islamic State movement in Iraq and Syria but has considerable operational independence,” notes Reuters.

Despite the losses with the Taliban, ISIS-K has proven to be a worthy opponent for their jihadi rival, considered the strongest group in Afghanistan.

The majority of the ISIS-K members are disgruntled Taliban fighters from the group’s offshoot in Afghanistan and Pakistan, with most belonging the Pakistani faction, the U.S. military has said.

Referring to the April 27 U.S. airstrike that took out the Afghan ISIS emir, a Pentagon spokesman revealed the following day that suspected ISIS-K jihadists had killed two American Army Rangers during a U.S.-Afghanistan operation, noting that Hasib may have also met his demise during the raid, without elaborating further.

The Afghanistan-based South Asia Islamic State branch, dubbed Khorasan (ISIS-K), is named after an ancient title of a region that covers Afghanistan, Pakistan, Iran, India, and other neighboring countries.

ISIS-K is believed to operate in most of the Khorasan countries, but the U.S. military has identified the group’s main stronghold as the opium-rich Nangarhar province.

Nangarhar may allow the ISIS terrorists to possibly generate funds from the lucrative but illegal opium business and likely enjoy sanctuary at and around the Afghanistan-Pakistan border where many terrorist groups are believed to find a safe haven.

The Pakistani government has claimed in recent months it is cracking down on ISIS after repeatedly denying the group’s existence on its soil.

Gen. Nicholson has accused and condemned Pakistan for joining Iran and Russia in lending support to the Afghan Taliban, all of whom claim they are just assisting the Taliban in their fight against ISIS.

Pakistan, Iran, and Russia do not enjoy the best of relations with the United States, before or after President Donald Trump was inaugurated as the new commander-in-chief.

“ISIS is believed to maintain links with the main Islamic State movement in Iraq and Syria but has considerable operational independence,” notes Reuters.

Since March, U.S. and Afghan special forces, backed by airstrikes, have been fighting to eradicate ISIS-K, primarily in Nangarhar.

Besides Nangarhar, the group is known to run a much smaller operation in northern Afghanistan’s Jawzjan province.

As part of the President Trump administration’s efforts to defeat ISIS, the commander-in-chief granted Gen. Nicholson and other top commanders more freedom to launch attacks against ISIS and other terrorists.

Last month, Gen. Nicholson authorized the use of the American military’s largest non-nuclear munition, dubbed the “mother of all bombs,” on a network of ISIL-K tunnels and caves in Nangarhar that made it difficult for the U.S. and their Afghan partners to combat the jihadists.

The U.S. military is believed to have executed more than 90 terrorists with the bomb, marking the first American troops used in combat.

U.S.-backed Afghan troops have recaptured at least half of the districts once controlled by ISIS-K.