Saudi Arabia and its coalition partners are preparing for a major offensive to take Yemen's capital from the Zaydi Houthi rebels this fall. If the battle becomes a house-to-house urban clash, it will have disastrous humanitarian consequences.

The Saudis are massing forces at two locations for the assault on Sanaa. To the east of the capital, coalition forces are preparing to attack in Marib province. According to press reports, 4,000 troops from the United Arab Emirates, another 1,000 from Saudi Arabia and Bahrain, and an unknown number of Yemeni loyalists are assembled for this offensive. Furthermore, south coalition forces in Taiz are preparing another move on Sanaa. Saudi and Emirati troops and Yemeni loyalists are reinforcing this axis as well.

The United Nations’ efforts to arrange a cease-fire this month were stymied by Yemen President Abed Rabbo Mansour Hadi’s refusal to attend peace talks in Oman unless the Houthis and their ally, former President Ali Abdullah Saleh, withdraw their forces from Sanaa and other cities first and accept UN Security Council Resolution 2216. Hadi remains in Riyadh, although some of his Cabinet members have moved to Aden where the situation remains unstable. A Saudi bombing attack damaged the residence of the Omani ambassador in Sanaa this weekend, sparking a sharp protest from Muscat.

The Saudi military successes in Aden and other fronts so far have been in Sunni inhabited parts of Yemen. Now they are moving into predominantly Zaydi Shiite areas. Sanaa itself is a city of 2 million people. Both the terrain and the local conditions will become more difficult for the coalition forces as the war moves toward Sanaa.