5 U.S. military members injured during operation
"We will continue to stay after Daesh until they are defeated here in Afghanistan," Nicholson said, using an Arabic acronym for the militant group.
Army General John Nicholson said the incident took place in the last few days in Nangarhar province, but did not specify exactly when it happened. Two of the injured service members have returned to duty, while three others were evacuated but are "in good spirits" and are expected to make a full recovery, he said.
"None of these are life-threatening injuries," Nicholson said in a briefing with reporters on Thursday. Their injuries were sustained from small arms fire and shrapnel, he added.
President Barack Obama in January gave U.S. commanders broader authority to target Islamic State fighters in Afghanistan. Since that time the territory controlled by the group has shrunk from about 10 districts in the southern part of Nangarhar province to parts of three or four districts, Nicholson said.
Also since that time, the number of Islamic State fighters has shrunk from 3,000 in January to 1,000 to 1,500 now, he said.
Most of Islamic State's fighters in Afghanistan previously fought for the Pakistani Taliban, or TTP, Nicholson said, and hail from Orakzai Agency in Pakistan near the Afghan border.
"They were former members of the TTP, complete with their leadership, who wholesale joined Islamic State ... earlier this year," Nicholson said. "Seventy percent, roughly, of those fighters are from the TTP and many of them are Pakistani Pashtun from the Orakzai Agency."
Other Islamic State members in Afghanistan were originally part of the Islamic Movement of Uzbekistan, another militant group, he said.
Last week more than 80 people were killed in a suicide attack in Kabul targeting Afghanistan's Hazara minority. The attack on Saturday, against a demonstration by the mainly Shi'ite Hazara, was among the worst in Afghanistan since the fall of the former Taliban regime in 2001, and was claimed by Islamic State.
Nicholson compared the bombing to recent attacks claimed by Islamic State in Europe and the United States, and emphasized that their footprint in Afghanistan was shrinking.
"The fact that they could conduct a high profile attack should not be perceived as a sign of growing strength," he said.
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