Clashes also broke out on the ground in several areas of the impoverished country in spite of UN calls for all sides to respect a ceasefire to allow desperately needed aid deliveries.
The Huthi Shiite rebels, who control swathes of Yemen including the capital Sanaa, said they had not been consulted about the truce that began at midnight (Sunday 2100 GMT).
The Arab regional coalition, which has waged four months of air strikes in support of exiled President Abedrabbo Mansour Hadi, announced the five-day ceasefire to allow emergency supplies to flow into the war-scarred nation.
Although there were no reports of air strikes on the rebels on Monday, military sources reported a "friendly fire" incident in which coalition warplanes hit positions of Hadi loyalists in the southern province of Lahj, killing 12 people.
Also Read
At least 30 others were wounded in the strikes on hills overlooking the rebel-held Al-Anad airbase, as well as in nearby Radfan, the sources said.
There was no immediate comment by the Saudi-led coalition.
Overnight the Huthis bombarded areas in the southern provinces of Taez, Lahj and Dhaleh, according to witnesses and military sources.
Loyalists were reported to have seized territory on the northern outskirts of Aden, after expelling the rebels from the southern port city last week following four months of ferocious fighting.
The pro-government forces have been bolstered by new weaponry and armoured vehicles delivered by the coalition.