At least 13 pro-government fighters were killed in a rebel attack on their positions near the Yemeni capital despite a UN-brokered ceasefire taking effect this week, military sources said on Thursday.
The rebels attacked positions of Gulf-backed loyalist fighters in Nihm, northeast of Sanaa, where clashes have occurred for two weeks despite warring parties promising to abide by a ceasefire that took effect on Sunday at midnight.
A number of Iran-backed rebels were also killed in fighting that erupted after the Wednesday attack, loyalist military sources said.
The fragile truce is meant to pave the way for peace talks next Monday in Kuwait.
Military sources said on Wednesday that rebels had killed a senior loyalist officer and wounded six troops in Nihm.
Two pro-government fighters and a rebel were also killed in other clashes east of Sanaa.
In the southern loyalist-held province of Shabwa, rebels fired a mortar round on a village, killing three children aged between six and 10, according to a provincial official.
Separately, Saudi-led coalition Apache helicopters struck suspected Al-Qaeda members on Wednesday in Huta, capital of the southern Lahj province, killing eight, security officials said.
The strikes targeted government buildings, a stadium and two homes where suspected jihadists were hiding, the officials said.
Saudi Arabia and its Arab allies are backing the Yemeni government in the conflict while Iran supports the rebel Houthis, who have seized Sanaa and other parts of the country.
Al-Qaeda and the Islamic State group have taken advantage of the chaos caused by the war to strengthen their grip on southern Yemen.
Forces loyal to President Abedrabbo Mansour Hadi have launched operations against jihadists in recent weeks, backed by the firepower of the Arab coalition.
The war has left more than 6,300 people dead since March 2015 and worsened living conditions, with more than 80% of the population now on the brink of famine.