SANAA Saudi-led air strikes hit Yemen's capital and another main city causing explosions, residents reported, two hours after a United Nations humanitarian truce took effect.
Bombing pounded Yemeni military positions east of the capital Sanaa and also Yemen's third largest city Taiz.
The U.N.-brokered pause in the fighting was meant to last a week to allow aid deliveries to the country's 21 million people who have endured over three months of bombing and civil war.
A coalition of Arab states has been bombing the Iranian-allied Houthi rebel movement since late March in a bid to restore to power Yemen's President Abd-Rabbu Mansour Hadi, who has fled to Riyadh.
The group controls much of Yemen, including Sanaa and Taiz.
Air raids and fighting have killed more than 3,000 people since then.
Residents in areas of heavy combat between Houthi forces and local militiamen reported that ground fighting and Saudi-led air strikes on the Houthis had increased across the country in the hours before the truce was to take effect.
All parties to Yemen's conflict had welcomed the announcement of the truce and called for it to be extended.
But the exiled government wants the group to release prisoners and give up land, while the Houthis say they doubt any calm would last.
"We don't have big hope in its success because its success is linked to the commitment of the Saudi regime and its allies," Abdel-Malek al-Houthi, leader of the Houthi movement, said in a televised speech on Friday.