With Yemen so divided, few expect the Geneva talks to hammer out a political transition or even pause the daily killings

* War locked in stalemate, Islamic State thrives in chaos

* Both sides score successes in battle

* U.S. fears Gulf Arabs preoccupied with Yemen, not IS fight

By Mohammed Ghobari and Noah Browning

DUBAI, Dec 14 (Reuters) - Alarmed by the rise of Islamic State, under pressure from the West and with stalemate on the battlefield, Yemen's civil war foes are expected to launch their most serious peace efforts so far at U.N.-mediated talks in Geneva starting on Tuesday.

The nine-month-old conflict between a Saudi-led Arab alliance and the Iranian-allied Houthis has outlasted two earlier U.N. attempts at peace making, caused one of the world's worst humanitarian crises and pushed Yemen towards total chaos.

Fuelling the urgency behind Tuesday's talks is a perception in the West that the war, in part a proxy contest between rivals Saudi Arabia and Iran, is a dangerous distraction diverting regional attention from what should be the pre-eminent task of fighting IS on its home turf and ending Syria's larger war.

"There is an opportunity now more than at any of the previous talks and negotiations to stop this war ... to confront terrorism and challenges," a spokesman for the Saudis' adversary, the Houthi militia group, Mohammed Abdul-Salam, said.

According to officials in the government of President Abd-Rabbu Mansour Hadi, Western countries are keen to avoid a power vacuum that could give jihadist militants the haven they now enjoy in the southern port of Aden and other lawless areas.

The newest branch of Islamic State has exploited the chaos to launch spectacular attacks in Yemen on both the Shi'ite mosques of the Houthis and senior officials and troops loyal to the government.

"In recent weeks, Washington and London have exerted intense pressure on President Hadi and the government side to make concessions and not to be extreme in terms of executing the Security Council Resolution," one senior Yemeni government official told Reuters.

"GULF STATES PRE-OCCUPIED"

The official was referring to a U.N. Security Council Resolution in April that called on the Houthis to quit the capital, Sanaa, and other cities they seized in late 2014 and early 2015.

"There's an international inclination toward preserving the Houthis and allowing them to continue having an active political role, especially in terms of ... confronting terrorism," the official said.

Unstable ever since a 2011 revolt toppled veteran president Ali Abdullah Saleh, Yemen finally plunged into civil war last year when the ex-leader joined forces with the Houthis to seize power, triggering a Gulf Arab military intervention.

Neither side has prevailed militarily and in the wake of a rash of attacks claimed by Islamic State, the United States has increased calls for the Gulf to divert their diplomatic and military attention away from Yemen back toward the militants' main base in Syria and Iraq.

"Saudi Arabia and the Gulf states joined the air campaign in the early days, but have since been pre-occupied by the conflict in Yemen," U.S. Defense Secretary Ash Carter told the Senate Armed Services Committee this month.

"I, too, wish that particularly the Sunni Arab nations of the Gulf would do more," he added.

Yemeni analyst Farea al-Muslimi said officials on both sides were cautiously optimistic about Geneva, amid unprecedented diplomatic pressure for peace, but hopes were not high of quick progress.

"Expectations are low in terms of finding a way for the Yemeni state to be put back together and finding an authority that could run the country," analyst al-Muslimi said.

"A longer-lasting ceasefire, the removal of the Saudi-led blockade on Yemeni ports and even a rough framework to keep the talks going is about as much as can be hoped for right now."

AIR STRIKES

The United Nations says at least 5,800 people, nearly half of them civilians, have been killed since Saudi-led air strikes began in March against the Houthis, who say they are conducting a revolution against what they call Hadi's corruption. More than 21 million people in Yemen require some kind of humanitarian assistance to survive - about 80 percent of the population.

Saudi and Emirati forces fighting alongside Hadi's loyalists in Yemen's south and east have made few significant gains since grabbing the port city of Aden.

Meanwhile, Houthi and Saleh forces have hit back by launching missiles at Gulf forces and held their own on the battlefield, although they appear unable to impose their writ on the whole country.

Previous talks have stumbled over Hadi's insistence that his foes immediately heed the United Nations and quit Yemen's population centres - an unlikely prospect given their dominance there.

But with Yemen so divided and its political classes polarised, few in the country expect the Geneva talks to hammer out a political transition and even pausing the daily killings would be considered a major accomplishment.

(Editing by William Maclean and Peter Millership)

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