At least 15 pro-government Yemeni soldiers were killed in rebel attacks in the north and in a suspected militant bombing in Aden on Sunday, military and security sources said.
Shia Huthi rebels and their allies launched twin attacks to try to retake the port of Midi in the northern province of Hajja, after loyalists had captured it, military sources said.
"Eleven soldiers were killed in the attacks and 28 others were wounded," a military official said.
Meanwhile, Saudi-led coalition warplanes carried out 15 air strikes against the Iran-backed rebels to stop their advance in the area, military sources said.
Other air strikes hit rebel positions in the insurgent-controlled capital Sanaa and other provinces over the past 24 hours, they added.
The sources spoke of rebel casualties but AFP could not verify this as the Huthis and their allies rarely acknowledge their losses.
The coalition began its war on the Iran-backed rebels in March 2015.
It intensified operations since the suspension in early August of UN-brokered peace talks between the rebels and their allies and Yemen's government.
Also on Sunday, in Yemen's main southern city of Aden, a roadside bomb killed four soldiers and wounded one at a checkpoint in the Sheikh Othman district, a security official said.
He said militants, who have boosted their attacks in government-controlled Aden over the past few months despite efforts to increase security, are suspected of being behind the bombing.
Earlier, the official had given a toll of two soldiers killed and three wounded but said that two later succumbed to their injuries.
More than 6,600 people have been killed in the Yemeni conflict since March 2015, the UN says.