The shelling of a camp for displaced people in Yemen's northwestern Hajjah province killed eight civilians and wounded 30 others, the United Nations said on Sunday, amid fears that a partial truce agreed last month could be in jeopardy."Parties to the conflict are obliged to do everything possible to protect civilians," said Lise Grande, humanitarian coordinator for Yemen. "The people who have fled their home to IDP (internally displaced person) sites have lost so much already. An attack like this cannot be justified - ever."The UN statement did not identify the source of the shelling, which occurred on Saturday.The war has largely been in a stalemate for years, with a Saudi-led coalition of Arab states and Yemeni allies unable to dislodge the Iran-allied Houthi movement that controls the capital and most major population centres.At recent talks in Sweden, the warring parties agreed a ceasefire in Hodeidah, the country's main port, but then failed to pull out their troops, a confidence-building step that could pave the way for political talks to end the almost four-year war.The truce has largely held but sporadic clashes intensified last week, with each side accusing the other of violating the deal.If fighting restarts in earnest around the port, the main supply route into the country could be cut off, leaving no way to feed millions of people on the verge of starvation.Wheat silos in Hodeidah were damaged by a fire caused by suspected mortar shelling, threatening food supplies for millions of hungry people, the United Nations said on Friday.