US President Joe Biden's point-man on Yemen arrived in Saudi Arabia on Tuesday for talks on a Houthi rebel offensive in oil-rich Marib province that could be a make-or-break battle in the seven-year war. Washington’s envoy to Yemen, Tim Lenderking, touched down in the kingdom for talks with Saudi and Yemeni officials to boost work towards a peace deal with Yemen’s Iran-aligned Houthi rebel movement. “Special Envoy Lenderking will discuss the growing consequences of the Houthi offensive on Marib, which is exacerbating the humanitarian crisis and triggering instability elsewhere in the country,” the State Department said. He will also “address the urgent need for efforts … to stabilise Yemen’s economy and to facilitate the timely import of fuel to northern Yemen, and the need for the Houthis to end their manipulation of fuel imports and prices inside of Yemen". Mr Lenderking's visit comes amid intensified fighting in oil- and gas-rich Marib, the government’s last stronghold in northern Yemen, and in Al Bayda province to the south, where Houthi militiamen have reportedly made gains in recent days. A study this week by the humanitarian analytics group ACAPS found that a Houthi win in Marib would displace half a million people and deliver a potentially fatal blow to Yemen’s exiled government by robbing it of $19.5 million each month in lost crude sales. “Now is the time to stop the fighting and enable Yemenis to shape a more peaceful, prosperous future for their country,” the group said. Deputy US Secretary of State Wendy Sherman was in Oman on Tuesday for talks with her counterpart, Sheikh Khalifa Al Harthy, on bringing about an “immediate, comprehensive ceasefire” in Yemen, another statement from the US government said. Yemen has been ravaged by war, disease and hunger since the Houthis seized the capital Sanaa and overthrew the government in 2014, drawing in a Saudi-led coalition the following year to restore the ousted leadership. The war has forced millions of Yemenis to flee their homes, claimed hundreds of thousands of lives and tanked the economy. Four fifths of Yemenis rely on aid, in what the UN calls the world's worst humanitarian crisis.