The United Nations expressed alarm on Saturday at the digging of new positions in Hodeidah by Houthi rebels and reports that drones are being used in direct contravention of a long-disputed ceasefire. The head of the UN’s observer mission said in a statement that progress made by the establishment of joint observation posts was under threat because of the apparent breaches. "The past days have witnessed reports of incidents involving the construction of new fortifications, movement of forces, and use of drones – all of which are in contravention of ceasefire agreements between the two parties," the statement said. Chair of the mission, Lt Gen Abhijit Guha, called on both parties to observe the ceasefire and to act in good faith to deal with incidents of escalation. It comes after Yemeni military officials said on Thursday that an international medical relief agency's hospital in western Yemen was hit in a Houthi drone and missile attack, causing huge explosions that left at least eight people dead. In a statement, Doctors Without Borders said they closed the hospital because of the attack and that there were no reports of deaths or injuries among its patients. They were transferred to other health facilities in the Red Sea city of Mocha. Wadah Dobish, a spokesman for Yemen's internationally recognised government, said the Houthi attack struck warehouses used by a government-allied force late on Wednesday, causing a huge fire. Doctors Without Borders, also known as MSF, says its hospital opened in August last year, offering free services to war-wounded people and surgeries. After five years of conflict, Yemen remains a divided country. The Iran-backed Houthis have controlled the capital, Sanaa, and much of the north since 2014. A Saudi-led, US-backed military coalition has fought against the rebels and backs the government of President Abdrabu Mansur Hadi. Mr Dobish, the government spokesman, said Wednesday's attack targeted government-aligned forces known as the Giants Brigade. He said at least three Houthi drones also took part in the attack, which caused huge explosions and fires that spread to residential areas. Mocha, historically famous for coffee exports, is in the south of Hodeidah province. The port in the provincial capital, also named Hodeidah, is Yemen's most important entry point for international aid. The port has been the centre of year-long, UN-brokered negotiations since December for a durable cease-fire to prevent the suspension of crucial aid deliveries. Wednesday's escalation could jeopardie the UN deal, criticised by observers as vague and hard to implement. The hospital in Mocha is basically the only functioning facility providing support to thousands of severely malnourished children, either from the area or from among those displaced who fled to Mocha over the past year to escape fighting in other areas. The escalation comes days after Mr Hadi and southern factions signed a new power-sharing deal to ends months of infighting in southern Yemen. The UN Security Council issued a statement on Wednesday hailing the power-sharing agreement as "a positive and important step towards a comprehensive and inclusive political solution for Yemen". Earlier, US Secretary of State Mike Pompeo tweeted that the signatories set an example for compromise to end the conflict and achieve stability in the war-torn country.