Five U.S. troops were wounded recently while fighting Islamic State militants in Afghanistan, the latest sign of an expanding U.S. mission in a war that just a few years ago appeared to be winding down.

The five American special operations troops were injured by small arms fire and shrapnel while conducting joint operations with Afghans in southern Nangarhar province, home to the Islamic State’s offshoot there in Afghanistan, defense officials said Thursday.

"I'd characterize it as a clearing operation," said Army Gen. John "Mick" Nicholson, the commanding general of U.S. forces in Afghanistan.

"They were clearing some of these areas ... in southern Nangarhar, where Daesh previously had control, and they were helping our Afghan partners to regain control of those areas," Nicholson told reporters Thursday, using an alternative term for the Islamic State group.

One of the troops was injured on July 24 and four were injured on July 25 in separate incidents, a defense official said. None of the injuries were life threatening, he added Nicholson said.

The operations in Nangarhar are an example of the expanding mission that President Barack Obama has approved this year for the roughly 10,000 U.S. troops who remain in Afghanistan.

In January, he gave American personnel U.S. forces there legal authority to strike the fledgling ISIS Islamic State faction under any circumstances. Then in In June, Obama approved U.S. air strikes and combat support for the Afghan army’s offensive operations against the Taliban.

The expanded authorities marked a significant shift from 2015, when the U.S. military was trying to reduce its role in direct combat and limit air strikes to situations where U.S. personnel were at risk.

"I've been using those authorities daily since the president gave them to us. Greatly appreciate those," Nicholson said.

"The new authorities, which essentially allow us to support [Afghan security forces] while in offensive operations … come in very handy, and really help them to maintain the momentum that they're gaining," Nicholson said.

The total number of bombs dropped in air strikes nearly doubled during the first six months of this year compared to the same six months last year. Air Force data shows 545 weapons released from January to June compared to 298 for the same period in 2015.

"And of course, using authorities does not always mean an airstrike," Nicholson said. "It may mean reconnaissance aircraft, it may mean armed reconnaissance, it may mean rotary-wing support. So, it enables me to use my combat enablers in support of the Afghans as they execute their strategic effects under their campaign plan."

Video: After 15 years, the Afghan army is no match for the Taliban

U.S. taxpayers are spending more than $4 billion annually to develop an Afghan security force whose progress has proven difficult to assess, according to a watchdog report to Congress.

Obama, several years ago, had hoped to end the U.S. military mission in Afghanistan before leaving the White House in January 2017. But the Afghan Army's progress came slower than once projected, and last year ISIS a faction of the Islamic State group emerged there.

The president Obama recently announced that he will leave 8,400 U.S. troops in the country when his term ends.

Most of the self-proclaimed Islamic State militants in Afghanistan are Pakistanis previously loyal to the Pakistani Taliban who adopted the ISIS Islamic State brand after they were pushed into Afghanistan by a Pakistani army offensive last year, Nicholson said.

He Nicholson offered an upbeat assessment of the fighting season so far. The Islamic State is loosing territory in Nangarhar, its primary stronghold, in Nangarhar and IS "retreating south into the mountains of southern Nangahar as we speak."

The estimated size of the Islamic State faction, last year around 3,000, is not closer to 1,000 to 1,500, the general said.

ISIS is one of nine militant groups operating in Afghanistan that is officially designated as a terrorist organization by the United States. The Taliban, the largest of those groups, has mounted several high-profile suicide attacks this year but has failed to gain new territory, Nicholson said.

The outlook is looking good even in Helmand province, where U.S. military officials were expecting a major Taliban offensive.

"Now, fighting season's not over. We anticipate we'll see other enemy attempts to regain territory in Helmand. But thus far, things are on a real positive trajectory," Nicholson said.

Nicholson noted that Afghan casualties are up about 20 percent compared to last year. But overall the Afghan Army's performance has improved, he said.

"They are doing some things very well this year, and we are seeing some progress."

But, he added, "the fight's not over."