Air strikes hit the Shiite Huthi stronghold of Saada in Yemen's north, as well as other positions south of the capital Sanaa and in the southern province of Lahj, residents said.

The UN-proposed humanitarian truce technically went into effect at 2059 GMT Friday and is supposed to run until July 17, the last day of the holy Muslim fasting month of Ramadan.

But the ceasefire, much needed to rush food supplies to a population threatened by famine, has been flouted by strikes conducted by the Saudi-led coalition and Saudi back terrorists fighting in the ground.

The ceasefire was declared after UN chief Ban Ki-moon received assurances from exiled Yemeni President Abedrabbo Mansour Hadi and the Huthis that it would be respected.

The coalition said it has not received a formal request from Hadi's government to observe a truce, while the huthis said before the ceasefire went into effect they had little hope it would succeed.

More than a week ago the United Nations declared Yemen a level-3 humanitarian emergency, the highest on its scale, with nearly half the country facing a food crisis.

More than 21.1 million people -- over 80 percent of Yemen's population -- need aid, with 13 million facing food shortages, while access to water has become difficult for 9.4 million people.

The UN says the Saudi attacks has killed more than 3,200 people, about half of them civilians, since late March.