Dozens of troops and militants have been killed in clashes in eastern Yemen, Yemeni security sources say.
Yemeni officials said soldiers were ambushed by al-Qaeda insurgents, while so-called Islamic State's (IS) Yemen branch said it carried out the attack.
At least 12 soldiers and 15 militants were killed in a gun-battle and suicide bombing near Shibam in Hadramawt province, reports say.
Yemen has for months been mired in a war compounded by militant attacks.
Large parts of Hadramawt, Yemen's biggest province, are under the control of al-Qaeda in the Arabian Peninsula (AQAP).
'Hours of fighting'
Yemeni security officials said masked men opened fire on pro-government troops and detonated a suicide car bomb at a checkpoint on Friday morning.
Fighting is reported to have gone on for hours afterwards.
Yemeni officials said AQAP had carried out the attack. However, IS' wing in Yemen - a rival of al-Qaeda - said it was behind the assault, which it said had killed 50 troops.
IS has carried out a string of bombings and attacks since the group emerged in Yemen in late 2014.
A Saudi-led coalition has been fighting Houthi rebels and its allies in Yemen since the government was forced into exile in March by a Houthi rebellion.
Since then, the fighting has left at least 5,700 people dead, about half of them civilians, the UN says.