The Houthi offensive that began earlier this month to seize Marib province, some 120 kilometers east of the capital, Sana’a, has met stiff resistance from troops of Yemen’s internationally recognized government. Marib is its last stronghold. Observers say the Houthis, a Zaydi Shi’ite movement fighting the Sunni Muslim-majority government, want to wrest control of Marib and its oil fields as well as close off Saudi Arabia’s southern border to give them leverage in possible peace talks. But they are also suffering heavy casualties.     The United Nations’ special envoy for Yemen, Martin Griffiths, said he was “extremely concerned” about the hostilities especially at a time of “renewed diplomatic momentum,” given the Biden administration’s decision to end support for the Saudi-led offensive and revoke the U.S. designation of the Houthis as a foreign terrorist group.  Kristin Diwan, a senior resident scholar at Washington’s Arab Gulf States Institute, says she believes that Saudi Arabia would like to extricate itself from the conflict. But the Houthis have also launched attacks on Saudi territory, showing increased daring and technical prowess.   “I think to some degree that Saudi Arabia is ready to make a deal and they scaled back what they were hoping to get out of this. If they can just get out with some security assurances," Diwan said. "The problem is exactly how do you get the Houthis to the table especially when they seem to be having the upper hand and are gaining. You can look and see what is happening around Marib and other places.” Ahmed Nagi, a nonresident fellow at the Malcolm H. Kerr Carnegie Middle East Center in Beirut, says international pressure for the Saudi-led war is needed beyond the Biden administration’s decision to end support.  “Day by day, bringing peace to the country seems elusive," Nagi said. "Today Saudi Arabia is suffering a lot especially the communities which are in the borders of the kingdom. The conflict in Yemen will be even harder without any sort of resolution. Ending the support is not enough because today the conflict in Yemen is not just between Saudi Arabia and some parts inside Yemen. It needs a comprehensive approach to tackle it.”   Yemen's war started in 2014, when the Houthis seized the capital and much of the country's north. A Saudi-led, U.S.-backed force intervened in 2015 to dislodge the Houthis and restore the internationally recognized government. The conflict has killed some 130,000 people and spawned what the United Nations calls "the world's worst humanitarian crisis.”