SANAA — Shiite rebels and their opponents battled across several provinces Monday after the start of a five-day humanitarian pause in the Saudi-led air campaign, Yemeni officials said. Coalition planes carried out flyovers over Yemen but did not drop munitions, the officials said. Ground fighting erupted in multiple provinces within minutes of the start of the unilateral ceasefire late Sunday. The Houthi rebels said in a statement that they fired missiles across the border at a Saudi military position in the Kingdom's Jazan region. The Saudi-owned Al-Hadath news channel said Saudi forces “responded” to Houthi shelling in Jazan, without elaborating. Fierce clashes also broke out in the nearby town of Sabr, which is on a key supply route. Officials aligned with pro-government fighters say they have regained control of the center of the town and trying to advance into northern neighborhoods. Officials and witnesses said there were sporadic clashes in Yemen's central Marib province. In Taiz, mortar shells fired in the center of the city killed four civilians, security and medical officials said. Anti-aircraft gunfire was heard in the rebel-held capital Sanaa as coalition planes buzzed overhead. The humanitarian pause is intended to help allow humanitarian aid to be delivered to ease the suffering of civilians in the Arab world's poorest country. 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, Abdrabbu 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. UN 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 toward it until then. “There is no positive or negative stance until the United Nations formally addresses us concerning the matter,” he said. — Agencies