After 11 weeks of airstrikes that have failed to change the balance of power in Yemen, Saudi Arabia is running out of options to restore President Abd-Rabbu Mansour Hadi's exiled government to Sana’a.
Despite the destruction of much of their heavy weaponry, the Houthi militia and army forces loyal to former president Ali Abdullah Saleh control most of the country's populated west and still daily attack Saudi territory with mortar fire or missiles.
The possibility of a ground operation in support of the ragtag local groups still fighting the Houthis in Aden, Taiz, Marib and al-Dhala appears to have been discounted by the Saudis and their allies in an Arab coalition from early on.
Riyadh may soon have to face an unpalatable choice: accept the de facto control of its foes over Sana’a and cut a deal, or keep fighting with the risk of Yemen sinking into total chaos, becoming a permanent threat to Saudi security.
U.N.-sponsored talks start in Geneva next week aimed at ending almost two months of war, which has killed more than 2,500 people, but there is little sign either Hadi or the Iranian-backed Houthis are ready to make compromises.
From a small frontier post on a desolate, windswept plateau overlooking the Saudi border town of Najran, the distant crump of explosions reminds the handful of soldiers surrounding two armoured cars that the Houthis remain entrenched nearby.
A mortar fell only 100 meters from their post a few hours earlier, the soldiers said, peering through binoculars at a flat-topped Yemeni mountain, dim in the ghostly afternoon haze.
Each night they watch the blasts from Saudi shells and missiles. That the militia's fighters have been able to continue lobbing mortar shells at Saudi border posts, killing over a dozen Saudi troops, shows how hard it is for even a superbly equipped military to defeat such mobile guerrilla forces.
Recent suicide attacks and shootings inside the kingdom also reveal the danger posed to Riyadh by Sunni Muslim jihadists, who have taken advantage of Yemen's chaos to consolidate a presence on the other side of the long, porous border.
Avoiding such disintegration in Yemen was a leading war aim of Riyadh, which believed the Houthi advance would accelerate sectarian divisions and end a Gulf-backed political process aimed at creating a stable, representative government.
"The U.S. is pushing the Saudis to accept talks but they are reluctant because they are in such a weak position on the ground in Yemen," said a diplomat who follows the matter closely.
Despite the fading prospect of political or military success inside Yemen, Saudi Arabia may still see its campaign as ultimately worthwhile for one big reason: Iran.
For years Riyadh has accused Iran of meddling in Yemen by backing the Houthi militia. Its accusations became louder when the Houthis exploited wider chaos last year to advance from its northern stronghold to the capital Sana’a, and then overrun the government and push south.
Most analysts believe Saudi fears of Iranian involvement in Yemen are overblown, and say Tehran has little control over the Houthis, but in the crucible of a wider struggle for influence, Riyadh could not accept its foe gaining power in Sana’a.
An Iranian member of parliament's boast last year that Sana’a had become the fourth Arab capital to fall to Tehran's influence after Baghdad, Beirut and Damascus when the Houthis took the city seemed to confirm Saudi fears.
When daily direct flights started between Tehran and Houthi-controlled Sana’a in January, Riyadh believed they were carrying weapons and other materiel that would ultimately threaten the kingdom directly. It was a turning point in their approach.
"You have to remember the situation three months ago. Without strikes, the Houthis would be everywhere. The Iranians would be more present than ever before. Right or wrong, this was their feeling," said a Gulf-based diplomat on Saudi thinking.
However, most senior Saudi figures now accept the military campaign can achieve little more and it is time for talks, even though the Houthis and Saleh hold the strongest cards by controlling swathes of Yemen, the diplomat said.
Both Riyadh and Hadi's exiled government are increasingly calling for the international community to enforce U.N. Security Council resolution 2216, which was approved in April and demands the Houthis quit Yemeni cities and hand over their arms.
"It is the responsibility of the international community and the security council," said Brigadier General Ahmed Asseri, the spokesman for the Saudi-led coalition, citing the example of Iraq's expulsion from Kuwait in 1991.
He added the coalition was focused on implementing 2216 because it offered the best chance of stabilizing Yemen long term. "It should be implemented to make sure of a final result to this situation. We have to think strategically," he said.
From the border post, where a tangle of scrub is the only sign of life on a steep slope of car-sized, pebble-smooth boulders, the chances of international intervention against a guerrilla army in Yemen's messy civil war look slim.
Riyadh is working with the exiled government to train some Yemeni fighters, but creating a proxy army that could roll back the Houthis and then establish stability would be a long-term undertaking with only precarious chances of success.
However, Saudi Arabia's continued bombing and insistence on implementation of 2216, which would in effect require surrender by the Houthis and Saleh, may be simply a precursor to talks, said the Gulf-based diplomat.
Riyadh has acknowledged from the beginning that the Houthis will be part of any eventual political settlement, but wanted them to be a minor player rather than a dominant one and for Hadi's government to return to Sana’a.
However, they may accept a deal that gives the exiled government some form of token return, alongside the Houthis, so long as the group's material links to Iran remain severed.
"From Saudi Arabia's point of view, that would mean the situation in Yemen was better than before its airstrikes began," the diplomat said.