NOORULLAH SHIRZADA via Getty Images Smoke rises after an air strike by US aircraft on positions during an ongoing an operation against Islamic State (IS) militants in Kot district of Nangarhar province on February 16, 2017.

WASHINGTON, April 8 (Reuters) - A U.S. soldier was killed while conducting operations against Islamic State in Afghanistan late on Saturday, a U.S. military spokesman said in a message posted on Twitter.

“The soldier was mortally wounded late Saturday during an operation in Nangarhar Province” in eastern Afghanistan, U.S. Navy Captain Bill Salvin said in a message on the official Twitter account of the NATO-led Resolute Support mission.

The soldier was a Special Forces operator, Salvin told Reuters separately.

The circumstances of the death were unclear and Salvin said more information could be released later.

Islamic State’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.

The Afghan Taliban, which is trying to overthrow the U.S.-backed government in Kabul, is fiercely opposed to Islamic State and the two have clashed as they seek to expand territory and influence.

(Reporting by Yeganeh Torbati and Idrees Ali; Editing by Leslie Adler and Bill Trott)