A five-day truce was declared on Saturday by the Saudi-led coalition bombing Yemeni rebels since March so aid can reach a country the UN says is on the brink of a humanitarian disaster.
Announcing the unilateral truce to begin from midnight on Sunday, a statement on the official Saudi Press Agency said the coalition also reserved the right to respond to "military activity or movement" by the Shiite Huthi rebels during the ceasefire.
SPA said the decision was taken at the request of Yemen's President Abedrabbo Mansour Hadi, who has taken refuge in the Saudi capital with much of his government.
Hadi, whose supporters have recaptured most of the southern port of Aden from the rebels after four months of war, wanted the truce for the "delivery and distribution of the maximum amount of humanitarian and medical aid", it said.
Two previous UN-brokered ceasefires failed to take hold.
The Saudi move came as Yemeni medical sources said a coalition air raid killed at least 35 civilians in the southwest of the war-ravaged Arabian Peninsula nation.
Women and children were among the dead in the Friday night strike on the town of Mokhba near the country's third city Taez, the sources said.
Residents said the raid hit a residential neighbourhood where employees of the town's power station live. They said several houses were destroyed and dozens of people were wounded.
Some witnesses said the district had been targeted by mistake, but others alleged that the Huthis had taken up positions in the area.
In March, the coalition began a campaign of air strikes after the Huthis swept into Sanaa and pushed south towards Aden, where Hadi initially took refuge before fleeing to Riyadh.
Coalition jets carried out fresh raids overnight on Huthi positions across Yemen, including around Aden, military sources said Saturday.
The United Nations says the conflict has killed more than 3,640 people, around half of them civilians, since late March.
On Friday, the International Committee of the Red Cross warned that civilian suffering in Yemen has reached "unprecedented levels".
The ICRC said intensifying violence in the south was hamstringing emergency medical aid.
It voiced particular concern over worsening clashes in the southern provinces of Taez and Aden.
"The suffering of the civilian population has reached unprecedented levels," ICRC mission chief in Yemen Antoine Grand said in a statement.
In Aden and Taez, "it is becoming increasingly difficult for us to reach affected areas, to evacuate the dead and the wounded and to provide life-saving assistance," Grand added.
The aid group urged both pro-Hadi forces and the Iran-backed rebels and their allies to let humanitarian groups work.
Aden's international airport was closed for months, but recent gains by Hadi loyalists allowed it to reopen this week.
Four aircraft carrying humanitarian supplies have since landed there, although the airport came under fire from rebels Thursday as a Saudi plane was unloading.
The ICRC warned that, as the fighting escalated, so too did "shortages of water, food and fuel across the country".
A boat chartered by the Red Cross and loaded with humanitarian supplies successfully docked at Aden Thursday.
The ICRC insisted that aid should not be held hostage by the shifting situation on the ground.
"All sides must facilitate our access and respect our mandate," it said.
A humanitarian ceasefire declared by the UN earlier this month was not respected, and the world body warned that the impoverished country was just "one step away from famine".