The Islamic State group in Afghanistan has lost considerable turf in the war-torn nation over the last year. The terrorist organization has fallen from a height of controlling 11 districts in Nangarhar province to just a few, according to Gen. John Nicholson, the U.S. commander overseeing operations in Afghanistan.

Operating primarily out of southern Nangarhar province, ISIS' primary goal has been the creation of a caliphate in Afghanistan, with Jalalabad as its capital. "This was their aspiration, but they failed to achieve it." Nicholson told lawmakers on Capitol Hill on Thursday.

Since authorities were granted to begin striking ISIS targets, the U.S. has conducted several major operations alongside Afghan forces, according to Nicholson. Those operations have had success pushing ISIS into only a small handful of districts and reducing their "geographic space," he said.

"We believe we've reduced their total end strength to less than 1,000 remaining in Afghanistan," said Capt. William Salvin, a spokesman for the train, advise, assist mission in Afghanistan.

However, ISIS is still a potent force with the ability to launch deadly suicide attacks in Kabul, Nicholson told senators.

"They have attacked Shia targets, primarily. They attacked at a peaceful demonstration, they've attacked at Shia mosques, they've attacked on Shia religious holidays," Nicholson explained.

Further complicating efforts to combat Islamic State fighters in Afghanistan is the sudden involvement of Russia in the Afghan conflict. Claiming to support the Taliban as a counter to ISIS expansion in the region, Nicholson sees a more nefarious objective from the Kremlin.

"I think it's to undermine the United States and NATO," Nicholson said when asked by Sen. David Perdue, R-Ga., about Russian intentions in the region. "This narrative that they promote is that the Taliban are fighting Islamic State and the Afghan government is not as fighting Islamic State and that therefore there could be spillover of this group into the region," Nicholson explained. "This is a false narrative."

Though the Taliban and ISIS see each other as rivals, conflicts between the two militant groups have not had the same effects as operations carried out by U.S and Afghan forces. "This year alone we have reduced their fighters by half, their territory by two thirds, we've killed their leader — in fact, their top 12 leaders — and continue to disrupt their operation," Nicholson added.

The core of ISIS fighters in Afghanistan hail from remnants of the Pakistani Taliban, referred to as the Tehrik-e-Taliban Pakistan (TTP), and other external foreign groups such as the Islamic Movement of Uzbekistan.

"I would comment that this group is universally rejected by the Afghan people. These are primarily non-Afghans in this group," Nicholson said.

On Sunday night, Afghan forces bolstered by U.S. airpower launched another major operation against ISIS in Nangarhar province, according to a report by Voice of America.

Shawn Snow is the senior reporter for Marine Corps Times and a Marine Corps veteran.