US and Afghan forces killed about 300 Islamic State (IS, or Daesh) fighters during a joint operation launched in Afghanistan’s eastern Nangarhar province, NATO Resolute Support Mission Commander Gen. John Nicholson said on Wednesday.

"[US and Afghan forces] killed a number of top leaders of the organization and up to 300 of their fighters," Nicholson told reporters.

Nicholson explained that the death toll represents about 25 percent of the estimated 1,200 Islamic State fighters in Afghanistan. Additionally, he said that Afghan forces have been more successful in fighting the terror group than they were last year.

The operation against the Islamic State, Nicholson noted, began about two weeks ago.

The Islamic State, which is outlawed in the United States, Russia and many other nations, gained a foothold in Afghanistan after infighting between Taliban factions broke out in 2015.

The group occupies a small territory inside Afghanistan, but has carried out a number of attacks, including one in the capital Kabul last month that killed more than 80 members of the Hazara minority sect.

In July, President Barack Obama announced he would leave 8,400 troops in Afghanistan by the end of his term in office instead of his original plan to leave 5,500 soldiers.