Saudi-led coalition had announced ceasefire for five days from Sunday to allow delivery of humanitarian aid
Yemen's Houthi group carried on fighting across Yemen on Monday despite a ceasefire announcement by its Saudi-led foes, and media controlled by the Iran-allied movement acknowledged that its forces had shelled targets inside Saudi Arabia.
The violence prolongs a four-month-old conflict rooted in political strains that spread across the Arabian Peninsula country last year, when the Houthis seized Sanaa and pushed aside President Abd-Rabbu Mansour Hadi, a US ally.
This angered the Sunni Muslim-ruled Gulf Arab states led by Riyadh, which regards the once obscure Houthis, who hail from Yemen's northern highlands, as terrorists.
The turmoil has made Yemen a front in Saudi Arabia's region-wide rivalry with Shi'ite Muslim power Iran, sometimes contested along sectarian lines, by creating an ally for Tehran in its backyard.
The Arab coalition fighting the Houthis had announced a five-day truce from 11:59pm local time on Sunday to allow in emergency aid amid severe shortages of fuel, food and medicine.
But the Saudi-owned Al Arabiya television reported Houthi forces shelled the northerly al-Tawal region on the Saudi border hours after the truce was meant to have started, and that Saudi forces had retaliated.
A senior Houthi official said his side had not been formally notified of any ceasefire by the United Nations.
The Saba news agency controlled by the Houthis said in a text message to subscribers that Houthi forces, and allies loyal to former president Ali Abdullah Saleh, had attacked places it named as al-Khawjarah and al-Maa'zab in the Red Sea province of Jizan with rockets and shells.
The war has killed more than 3,500 people. U.N. children's agency UNICEF says the death toll includes 365 children.
Yemen's capital Sanaa, the target of near-nightly air raids during the war, passed a quiet night.
In a heavily bombed district of Sanaa, a nine-year-old girl, wearing a pink dress and holding her father's hand, said: "Today I walked out to the cornershop to buy chocolate without fear ... We want this war to stop and return to our school."
Jamil, 40, owner of an car service shop in Sanaa's Nahedeen district, said a five-day ceasefire "doesn't change anything ... but we and our children were able to sleep without air raids last night for the first time in a long time."
Elsewhere, the violence continued.
In the country's second city, Aden, residents said Houthi forces had fired missiles at the Mansoura and Sheikh Othman districts from shortly after midnight until after dawn.
The Sabanew.net website, loyal to the Saudi-backed Yemeni president, Abd-Rabbu Mansour Hadi, said Houthi militias had shelled several residential communities in the southern town of Dalea, about 170 km (105 miles) north of Aden.
The Saudi state news broadcaster Ekhbariya reported that Houthi forces had carried out attacks in the central province of Marib and central city of Taiz.
U.N. Secretary-General Ban Ki-moon urged all parties on Sunday to suspend military operations during the pause and refrain from exploiting it to move weapons or seize territory.
Shortly before Ban's statement, the head of the Houthi supreme revolutionary committee, Mohammed Ali al-Houthi, said the group had not been informed by the United Nations about the truce and would not form a position towards it until then.
"There is no positive or negative stance until the United Nations formally addresses us concerning the matter," he said.