The United Nations special envoy for the conflict in Yemen warned UN ambassadors on Tuesday that a fledgling peace process was hanging by a thread. At the weekend Yemen's Saudi-backed government and Iran-backed Houthi rebel's wound up peace talks in Switzerland without a breakthrough. On the ground ceasefire violations are continuing even as UN humanitarian agencies warn that civilians are under fire and living in desperate conditions. "The talks revealed deep divisions between the two sides on the path to peace and the shape of a future agreement... trust between the parties remain weak," UN envoy Ismail Ould Cheikh Ahmed warned. Ahmed called for a stronger ceasefire agreement and urged UN member states to support his efforts to mediate a dialogue in the run-up to renewed talks next month. "I have to admit that there were several days when I feared that the two sides would not find a way to make progress on any of the central issues," the ambassador said. "We all know that the path to peace in Yemen will be a long and difficult one — but we also know that failure is not an option," he insisted. Meanwhile, unidentified gunmen shot dead a colonel in Yemen's southern resistance in Aden on Tuesday night, a local official said, the latest in a string of assassinations in the city often carried out by militants. The gunmen opened fire on a car containing resistance leader Jalal Al-Awbali in the Dar Saad district of northern Aden, killing him immediately, the official said. Militants from both Al-Qaeda in the Arabian Peninsula (AQAP) and the Yemeni wing of the Daesh (the so-called IS) group have staged attacks throughout southern parts of Yemen, including in Aden, for years. The rate of attacks in Aden has accelerated since July, when local forces backed by the government of President Abdrabbu Mansour Hadi and a Saudi-led military alliance recaptured the city from the Houthi militia after months of street fighting. Insecurity in Aden, the biggest prize yet won by Hadi in Yemen's nine-month civil war, threatens to undermine the campaign waged on his behalf against the Houthis and army units loyal to former president Ali Abdullah Saleh. In a sign of growing international concern over Yemen's security problems, a US drone strike killed four suspected AQAP militants in central Yemen on Tuesday, the first such attack since September. — Agencies