SANAA Yemen's Houthis toughened demands for the resumption of talks to end the 19-month-old civil war, saying President Abd-Rabbu Mansour Hadi must go and an agreement must be reached on the presidency.
The comments from the Iran-aligned forces are likely to complicate United Nations efforts to bring the parties back to talks based on proposals made by U.S. Secretary of State John Kerry in August.
Hadi's internationally-recognised government, which is supported by an alliance of Arab states led by Saudi Arabia, is battling the Houthis who took over the capital Sanaa in September 2014.
"Any talks or negotiations by Yemeni delegates must be on the condition that the United Nations offers a written and comprehensive peace plan," delegates from the Houthis and former president Ali Abdullah Saleh said in a statement on Saba news agency.
"If the proposal does not include an agreement on the new presidential institution, then it [the U.N. peace plan] becomes merely a partial and incomplete vision, which cannot be a foundation for discussion," the statement said.
A shaky ceasefire between the government and the Houthis, who practise a variant of Shi'ite Islam, took effect in April and brought some respite from the war, which started when the rebels pushed the government into exile in March 2015.
Peace talks broke down in August, though, and Saudi-led air strikes on the Houthis have resumed.
U.S. Secretary of State John Kerry said on August 25 he had agreed in talks with Gulf Arab states and the United Nations on a plan to restart peace talks with a goal of forming a unity government.
The final agreement would also include the withdrawal of forces from Sanaa and other areas and the transfer of heavy weapons the Houthis and forces allied to them to a third party, Kerry said at the time.
In another development, the United Nations' aid chief said the organisation needed the rapid cooperation of Yemen's various authorities to fight malnutrition that is afflicting millions.
UN emergency relief coordinator Stephen O'Brien, in a Reuters interview on a visit to Yemen, also said that damage to infrastructure, including cranes at the main Hodeidah port, had affected shipments of food, fuel and medicine to Yemen.
"Of course we need to do so much more, what we are doing we know to be insufficient," he said. "The authorities, whoever they are, need to able to give us great and quick facilitation, not put administrative burdens in our way, not to distrust us."
Yemen relies almost solely on imports, but the war has slowed shipments to a trickle. Out of 28 million Yemenis 21 million need some form of humanitarian aid and at least half the population suffer from malnutrition, the U.N. has said.
Speaking after visiting aid efforts, O'Brien said it was "absolutely terrifying" to see thin, malnourished babies in the paediatric and feeding wards of a hospital.
"These things are avoidable. And that's why we need to get not only food but medical items in, because the other thing that is almost obliterated is the health service.
O'Brien urged Yemeni authorities to facilitate U.N. work by issuing visas to staff and removing administrative obstacles.
He said that a verification and inspection mechanism set up by the United Nations had helped ease transport of vital food and medical supplies to Yemen but damage to Hodeidah port and its facilities was slowing down the process.
"Of course its terrible to see the smashed cranes which limit the capacity to be able to unload the ships along side the berths to bring in the food supplies and the fuel that is so necessary," O'Brien said.
(Reporting by Mohammed Ghobari, writing by Hadeel Al Sayegh and Sami Aboudi, Editing by William Maclean and Angus MacSwan)