Fierce clashes broke out in Yemen's crucial port city of Hodeidah on Sunday, leading UN and Yemeni officials to delay the "official" start of the hard-fought ceasefire agreed last week. Residents reported skirmishes on the outskirts of town with missiles and automatic gunfire heard near the city's eastern 7th July suburb. Unconfirmed television reports said that the Saudi-led coalition had launched two airstrikes on Ras Isa, a port north of Hodeidah. On Thursday, the Iran-aligned Houthi rebels agreed to a UN-brokered truce in Hodeidah with the Saudi-led coalition that backs the official government of Abd-Rabbu Mansour Hadi. UN officials said it was necessary to delay the implementation of the ceasefire until December 18th to convey orders to troops on the ground. On Sunday afternoon, UN Yemen envoy Martin Griffiths issued a plea to both to "respect their obligations as per the text and the spirit of the Stockholm Agreement" and "engage in the immediate representation of its provisions." "Without peace, we will be facing in 2019 a much worse situation than today" as a result of food shortages, warned UN chief Antonio Guterres on Sunday. Hodeidah is almost completely controlled by the Houthis, and their withdrawal from key positions like the port is one of the central components of the UN-brokered deal reached last week in Sweden. By moving units away from the Red Sea port, international officials hope to get desperately needed food and aid into the country to ease Yemen's festering humanitarian crisis. Under the deal, which could create the breathing space for meaningful peace talks, international monitors are to be deployed in Hodeidah to observe as all armed forces pull back completely within 21 days of the start of the ceasefire. Skirmishes and clashes like those seen in Hodeidah over the past two days are not in themselves a sign that the ceasefire is doomed, said independent Yemen analyst Hisham Al-Omeisy. "Even in previous ceasefires, there was a huge de-escalation infighting, but still sporadic fighting here and there, like we've seen over the past few days," he told the Telegraph. He cited recent conversations with Houthi contacts where the atmosphere in Hodeidah was cited as "toxic" and characterised by a deep mistrust of the Saudi-led coalition. A rise in looting by Houthi forces, he said, showed "bad faith" ahead of the agreed withdrawal.