Two U.S. service members were killed during an operation against Islamic State militants in eastern Afghanistan overnight on Wednesday, a Pentagon spokesman said on Thursday.

The incident took place in the southern Nangarhar province, Pentagon spokesman Captain Jeff Davis said.

U.S. troops are battling suspected Islamic State militants in Nangarhar province, near the border with Pakistan, where earlier this month, the United States dropped a massive bomb known as "the mother of all bombs."

Earlier this month, another U.S. soldier was killed while carrying out operations against Islamic State in Afghanistan.

The Islamic State militant group's offshoot in Afghanistan, known as the Sunni jihadist group's so-called Khorasan Province, is suspected of carrying out several attacks on minority Shi'ite Muslim targets.

U.S. officials say intelligence suggests Islamic State is based overwhelmingly in Nangarhar and neighboring Kunar province.

Estimates of its strength in Afghanistan vary. U.S. officials have said they believe the movement has only 700 fighters but Afghan officials estimate it has about 1,500.