Yemen's Prime Minister Khaled Bahah on Tuesday called on Houthi rebels to lay down their weapons as a ceasefire in his war-wracked country came into force and UN-brokered peace talks began in Switzerland. "We need to restore the country," Bahah said in the Qatari capital Doha. "We need the Houthis to surrender their weapons and arms and leave the government institutions to restore legitimacy." Bahah was delivering a speech at Qatar University coinciding with the start of a seven-day ceasefire as UN-brokered peace talks opened in Switzerland. Limited violations of the truce were reported shortly after a ceasefire began at midday (0900 GMT), with several mortar rounds hitting government forces in the southwestern province of Taiz, according to a Yemeni security official. The Saudi-led coalition, which launched an air war against the Houthi rebels and their allies in March, said the ceasefire had started as scheduled following a request by Yemeni President Abdrabbu Mansour Hadi. The rebel forces, who control the capital, have yet to say if they will abide by the truce. The UN envoy to Yemen, Ismail Ould Cheikh Ahmed, hailed the halt in fighting as "a critical first step towards building a lasting peace in the country." He said that the talks in Switzerland "seek to establish a permanent ceasefire and pave the way for a return to a peaceful and orderly political transition." UN spokesman Ahmad Fawzi confirmed that the talks had begun at an undisclosed location. "The UN-sponsored consultations aimed at finding a durable settlement to the Yemen crisis started today in Switzerland," he told reporters. "These consultations seek to establish a permanent and comprehensive ceasefire, secure improvements to the humanitarian situation and a return to a peaceful and orderly political transition," he added. Fawzi said 12 negotiators and six advisers made up each of the two delegations taking part in the talks. Ahead of the truce, clashes shook the flashpoint city of Taiz and coalition warplanes bombed rebel positions. Even after the ceasefire took effect, a Yemeni security official reported five mortars targeted pro-Hadi forces in Shuraija, south of Taiz. The coalition has warned that it "reserves the right to respond in case of any violation." Hadi has declared his government's intention to have a seven-day truce to coincide with the peace talks and to be "renewed automatically if the other party commits to it," the coalition said. A Yemen presidential statement said the proposed ceasefire "comes out of keenness to grab any chance to achieve peace, to reduce the suffering of our people in Yemen and to end bloodshed." Meanwhile, the World Health Organization (WHO) said that the warring parties in Yemen have promised it "unconditional movement" of supplies and medical teams under the UN ceasefire that came into effect throughout the war-torn country on Tuesday. Nineteen trucks pre-loaded with medical supplies in Aden and Sanaa are due to begin moving later in the day to start distribution across Yemen, WHO representative Ahmed Shadoul told a news briefing in Geneva. Some 150 metric tons of supplies in WHO's warehouse in Djibouti are expected to be shipped to Sanaa on Dec. 21 or 22, he said. From there, ships will take them to other Yemeni ports. "It depends on access, we will plan more if access is really granted. This is just a test," he said.