At least half of Islamic State's fighters in Afghanistan have been killed in the last six months, bringing the terrorist group's total number to around 1,000 to 1,500, according to the commander of US forces in the country.
Army Gen. John Nicholson, the commander of Resolute Support and United States Forces in Afghanistan, said the Americans were helping Afghan special operators "regain control" of areas recently held by ISIS in Nangarhar province, eastern Afghanistan.
Nicholson said two of the USA soldiers had returned to duty and the other three were evacuated but were "in good spirits".
In January, President Obama gave additional authorities to ground commanders in Afghanistan, allowing them to target the growing cell of Islamic State fighters in the country's east.
In a video briefing from Kabul to the Pentagon, Nicholson said the US casualties occurred during an ongoing offensive by the Afghan National Defense Security Forces to rout ISIS from Nangarhar.
"Some of our servicemembers have been wounded in this operation, a total of five", Nicholson stated. adding that that the USA special operators sustained injuries from small arms fire and shrapnel.
He said ISIS' force had been reduced from an estimated 3,000 fighters to about 1,500.
"We will continue to stay after Daesh until they are defeated here in Afghanistan", Nicholson said, using an Arabic acronym for the militant group.
The bombing was by far the Islamic State's deadliest attack in the country to date, and the worst in the capital since the Taliban was ousted in 2002.
Nicholson said a "significant proportion, a majority of fighters" with IS in Afghanistan come from Pakistan's Orokzai agency, over the border from Nangarhar, and are former members of the Tehrik-i-Taliban Pakistan, or TTP, also known as the Pakistani Talban.
Other Islamic State members in Afghanistan were originally part of the Islamic Movement of Uzbekistan, another militant group, he said.
It comes days after a bomb attack in Kabul claimed by IS killed eighty people.