Two U.S. service members died during operations against the Islamic State in eastern Afghanistan, the Pentagon said on Thursday.

A Pentagon spokesman, Capt. Jeff Davis, said the deaths occurred overnight in Afghanistan’s Nangahar province, where a small but virulent Islamic State cell poses a threat for Afghan and U.S. coalition forces.

It was the third time this year that a member of the U.S. military has died in combat in Afghanistan. On April 8, Army Staff Sgt. Mark De Alencar, 37, was mortally wounded by small-arms fire, also in Nangahar.

The deaths come just days after Defense Secretary Jim Mattis visited Afghanistan to assess the security situation and advance deliberations about the Trump administration’s strategy for America’s longest war.

The commander of U.S. troops in Afghanistan, Gen. John Nicholson, has called for thousands of additional troops to help prop up the Afghan military, which is struggling to hold off the Taliban and an array of other militant groups.

A local branch of the Islamic State, comprised mainly of militants pulled from other groups, has emerged as an increasing focus for U.S. forces remaining in Afghanistan.

While military officials say the group is far smaller than it was at its height in 2015, an estimated 600 to 800 militants located mainly in remote mountainous areas have proven to be a deadly adversary. Fighting has been fierce as U.S. and Afghan Special Operations forces, backed by hundreds of airstrikes, have sought to advance against militant strongholds in recent months.

Earlier this month, U.S. forces in Afghanistan dropped a 22,000-pound guided bomb called a GBU-43 on an Islamic State tunnel complex in Nangahar, the first use of a weapon of its kind.

While Afghan officials said between 36 and roughly 100 Islamic State fighters were killed in the strike, the U.S. military has not announced what exactly the massive bomb accomplished. Local media reports indicate that fighting around the blast site continues, and it was not immediately clear whether Thursday’s casualties occurred near that location.