The US military said it killed dozens of ISIL fighters at the group's training camps in central Yemen, in the first such strikes in the country's conflict.
Witnesses said villagers were prevented by tribal leaders from approaching the area and retrieving the dead and wounded for fear of additional strikes.
Locals said the camps, both in Bayda province, were named after prominent ISIL figures: Yemen chief Abu Bilal Al Harbi and former global spokesman Abu Mohamed Al Adnani, killed last summer in a US air strike.
This is the first time allies of Yemen's internationally recognised government have announced raids against ISIL footholds.
"US forces killed dozens of ISIS members in a strike on two ISIS training camps … in Al Bayda Governorate, Yemen, disrupting the organisation's attempts to train new fighters," US Central Command, which oversees US forces in the region, said in a statement on Monday.
"ISIS used the camps to train militants to conduct terror attacks using AK-47s, machine guns, rocket-propelled grenade launchers and endurance training."
ISIL and its jihadist rival Al Qaeda have taken advantage of a conflict between the government and Shiite Huthi rebels, who control the capital Sanaa, to bolster their presence across much of the south.
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The US is the only force known to operate armed drones over Yemen, but previous known strikes have exclusively targeted Al Qaeda.
ISIL, however, has risen to prominence in the country's civil war targeting both army recruits of the government and Shiites, which it considers heretics.
It entered the war in March 2015 with a series of attacks on Shiite mosques in the capital, leaving more than 140 people dead.
The group's last major attack was a suicide bombing in the government stronghold of Aden last December, which killed 48 soldiers.
"Strikes against ISIS targets disrupt and destroy militants' attack-plotting efforts, leadership networks and freedom of maneuver within the region," the statement read.
Al Qaeda has distanced itself from ISIL attacks, claiming that it seeks to avoid "the shedding of any Muslim blood" while focusing on fighting the "Americans and their allies".
The Saudi-led coalition, which intervened in Yemen in March 2015 to roll back Huthi rebel gains, has also turned its firepower on Sunni jihadists and backed forces loyal to president Abdrabu Mansur Hadi.
The Yemen war has killed 8,673 people and wounded 58,636 — among them many civilians, according to the UN.
"ISIS has used the ungoverned spaces of Yemen to plot, direct, instigate, resource and recruit for attacks against America and its allies around the world," the statement said.
"For years, Yemen has been a hub for terrorist recruiting, training and transit."
