Parties including the powerful Huthis have agreed on the "form of the legislative authority in the interim period", Benomar wrote on his Facebook page yesterday.
He hailed the preliminary accord as an "important step towards achieving a comprehensive political agreement that would end the current crisis".
The Huthis seized Sanaa in September before tightening their grip and prompting Western-backed President Abedrabbo Mansour Hadi to offer to resign in protest.
They dissolved parliament and installed a "presidential council" on February 6, sparking security concerns that saw several Arab and Western states close their embassies and evacuate diplomats.
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Half of the seats in the new council would go to representatives of formerly independent South Yemen, while women and youth groups would get a 30 percent and 20 percent quota respectively.
The two chambers together would form the "national council," the UN envoy said.
"This progress is not an agreement, but is an important breakthrough that paves the way towards a comprehensive agreement," he wrote.
In a new resolution, adopted unanimously by all 15 members, the council also demanded that the militia release Hadi, his Prime Minister Khalid Bahah and other officials and activists under de facto house arrest or in detention.
In response on Monday, the Huthis told the Security Council to "respect the will and sovereignty of the Yemeni people, and to be accurate and objective".
Since overrunning Sanaa unopposed in September, the Huthis have since expanded their control to coastal areas and regions south of the capital, but have faced fierce resistance from Sunni tribes and Al-Qaeda militants.
One soldier was killed and four were wounded in a roadside bombing in Hadramawt province today.
The attack on the road between the main interior towns of Sayun and Shibam targeted the convoy of General Abdulrahman al-Halilli, commander of the First Military Region, an army official said.