Yemen's warring factions want to make military advances on the ground before accepting a humanitarian pause proposed by the UN at deadlocked negotiations in Geneva, experts say.
So far, no advances have been made at the talks, expected to wrap up Friday, with both the Iran-backed Huthi rebels and the Saudi Arabia-supported exiled government sticking to their guns.
"Neither side has exhausted its military options, and they both think they could achieve more gains on the ground," said April Alley, a Yemen specialist with the International Crisis Group.
UN special envoy for Yemen, Mauritanian diplomat Ismail Ould Cheikh Ahmed, has been frantically shuttling between the hotels housing the two delegations to convince them to declare a halt in the relentless violence.
If it can't achieve that, the UN hopes to at least get them to agree to a 15-day humanitarian truce.
UN Secretary General Ban Ki-moon launched the high-stakes negotiations on Monday with an appeal for a two-week humanitarian truce during the holy Muslim month of Ramadan.
The negotiations, in their fifth day, have been bogged down by the government's insistence that the rebels must withdraw from the vast territory they control, including the capital Sanaa.
The rebels have overrun much of the Sunni-majority country and, along with their allies including forces loyal to ousted president Ali Abdullah Saleh, have been the target of Saudi-led air strikes since March.
More than 2,600 people have been killed since then and some 21 million Yemenis are in urgent need of humanitarian aid.
The rebels meanwhile are demanding an unconditional halt to the air strikes before they will consider a pause in fighting.
A source close to the negotiations however said that on Thursday they seemed prepared to consider withdrawals from the southern city of Aden and central city of Taez, far removed from their northern stronghold.
Since they entered Sanaa last September, the Huthis, members of the Zaidi sect of Shia Islam, have swept through the country, forcing President Abedrabbo Mansur Hadi into exile in Saudi Arabia.
Their massive advances were made possible by their alliance with ousted president Ali Abdullah Saleh, who ironically fought them while he was in power.
A Western diplomat following the Geneva talks compared the alliance to "a marriage of convenience", where each side brings something to the table.
The rebels, he said have "their determination, their local expertise, their support" from the local population and tribes.
The Saleh camp meanwhile has elite troops, heavy weaponry and a sophisticated communications network, he added.
Mustafa Alani, an analyst with the Gulf Research Center, said the Huthis have between 15,000 and 20,000 fighters on the ground, trained by the Iranians and Lebanese Hezbollah.
However, he said, since the beginning of the airstrikes, they "are no longer receiving military aid from Iran."
There are also around 70,000 elite troops on the ground, he said, but stressed that it remained unclear how many of them remain loyal to Saleh.
Hadi meanwhile "has no tribal base and is not strong within the army," Alani said, pointing out that troops loyal to the exiled president were fewer and not as well-equipped as those fighting on the other side.
Instead, Hadi is relying on the Saudi-led airstrikes to weaken his opponents, he said, pointing out that the bombing raids are knocking out rebel side's communications networks and destroying their heavy weaponry.
But the almost daily air strikes have not shifted the balance on the ground, and have not halted the rebel advance, the Western diplomat said.
The rebels, who have no experience in power or international negotiations, said Thursday they wanted the country to hold elections.
"We hope these preliminary talks will end up in some kind of accord... a transition that will hopefully lead to free, fair and transparent elections," the head of the rebel delegation Hamza al-Huthi told reporters.
"Huthis have always had ambiguous, evolving demands over time," Alley said.
Meanwhile, the UN is preparing to announce a new round of talks in Geneva, the delegates hinted.