At least three soldiers were killed in clashes with al Qaeda militants in southern Yemen in an operation launched by the internationally recognised government of President Abd-Rabu Mansour Hadi, security sources said.
They said at least 10 other soldiers were wounded when troops were ambushed east of the coastal city of Shuqra on Tuesday. Intense clashes were continuing on Wednesday.
The sources said that Hadi forces, backed by aircraft of a Saudi-led coalition, were targeting Shuqra when they were surprised by the militants. One military vehicle overturned, another was destroyed and two were captured, they said.
The incident highlighted the obstacles facing Hadi's government as it struggles to wipe out al Qaeda while simultaneously trying to defeat Houthi fighters in a war that has lasted nearly two years and killed more than 10,000 people.
In August, the Yemeni army drove al Qaeda out of two strongholds in the same region in a campaign in which at least 40 militants were killed.
The United States, which sees the Yemeni branch of al Qaeda as a threat to its own security, said last month it had killed 28 militants in nine strikes in the Arab country since September.
The group has exploited the civil war between Hadi's Saudi-backed government and the Houthis, aligned with Iran, to recruit followers and expand its influence across the country, especially in the south and east.
The impoverished country overlooks key shipping routes and shares a long border with Saudi Arabia, the world's top oil exporter.
In other parts of Yemen, clashes were reported between Hadi supporters and fighters from the Houthi group and their allies in the southwestern city of Taiz, the northern province of Saada and in Shabwa in the southeast.
The Hadi-run sabanew.net news agency reported "major gains" in Shabwa province, but residents said that the battlefront had changed little in other parts of the country.
Newly recruited Houthi fighters chant slogans as they ride a military vehicle during a gathering in Sanaa to mobilise more fighters to battlefronts to fight pro-government forces in several Yemeni cities.