(Adds 3 wounded in Turkey; Patriots; Saudi comments)
* Fuel and food shortages worsen hardship
* Rebels destroy minorities' religious sites - HRW
* Russia says no peace unless opposition talks to Assad
By Catherine Hornby and Alexander Dziadosz
ROME/BEIRUT, Jan 23 (Reuters) - Syria's 22-month civil war has ravaged vital infrastructure and halved the output of staple crops, the United Nations said on Wednesday, underscoring the lasting damage from which the country will take years to recover.
What began as a peaceful protest movement against President Bashar al-Assad has killed more than 60,000 people, devastated the economy and left 2.5 million people hungry.
Prospects of a negotiated peace have receded as the war becomes more overtly sectarian, making Western powers more wary of supporting the largely Sunni Muslim, and increasingly radicalised, rebellion.
Human Rights Watch on Wednesday pointed to the burning and looting of religious sites of minorities in recent months that suggested an escalation of sectarian strife.
As fighting raged throughout the country, Assad's most powerful foreign backer Russia said the war would not be resolved peacefully as long as rebels insist on his overthrow.
Detailing the damage from the longest and deadliest of the Arab uprisings, the U.N.'s Food and Agriculture Organisation (FAO) said wheat and barley production in Syria had dropped to 2 million tonnes in 2012 from 4-4.5 million tonnes in normal years.
Agriculture is vital to the economy, accounting for roughly a fifth of gross domestic product before the war.
A U.N. assessment in Syria this month, coordinated with both Syria's government and the opposition, found the conflict was destroying infrastructure and irrigation systems and that insecurity and fuel shortages were making it harder for farmers to harvest crops.
The devastation to farming could push the government to spend more money on food imports, further straining the resources of a country that officials said was self-sufficient in wheat before the conflict.
"The mission was struck by the plight of the Syrian people whose capacity to cope is dramatically eroded by 22 months of crisis," Dominique Burgeon, director of FAO's Emergency and Rehabilitation Division, said in a statement.
"Destruction of infrastructure in all sectors is massive and it is clear that the longer the conflict lasts, the longer it will take to rehabilitate it," he said.
Power cuts and fuel shortages have become part of daily life and residents of central Damascus, which had been spared the worst fallout of the war, say basic services are breaking down.
Drivers in Damascus said there had been no petrol in the capital for two days.
A black market for fuel has developed in which traders charge roughly 20 percent more than government prices, residents said. Some also reported food shortages in the city centre.
Severe shortages have also hit other parts of Syria, especially rebel-held areas subjected to daily bombardment by government artillery and warplanes.
Assad and his family, who have ruled the country for more than four decades, belong to the minority Alawite sect, an offshoot of Shi'ite Islam. Syria is also home to Christians, Ismailis, Druze and other minorities.
New York-based Human Rights Watch pointed to a video published online in December that showed rebels waving assault rifles and cheering as a Shi'ite place of worship in the northern village of Zarzour burned in the background.
In the video, which Reuters cannot independently verify, one man announces the "destruction of the dens of the Shi'ites and Rafida", a derogatory term used to describe Shi'ites.
Rebels also clashed with Kurdish People's Defence Units in the northern border town of Ras al-Ain on Wednesday, a monitoring group said.
Fighting there has killed more than 56 people over the last week as insurgents brought in heavy weapons including tanks and mortars to attack the Kurdish militants, the Britain-based Syrian Observatory for Human Rights said.
A Turkish official said three people had been wounded in the past week - one of them critically - by gunfire in the Turkish town of Ceylanpinar, just across the border from Ras al-Ain.
Ankara has repeatedly scrambled jets along the frontier and has responded in kind when shells originating in Syria have landed within its borders.
The first Patriot missile batteries being sent by NATO countries to shield Turkey from possible missile attack from Syria are expected to be in place and ready for use this weekend, a senior officer in the Western military alliance said.
RUSSIA STANDS FIRM
Russia, which has a naval base on Syria's Mediterranean coast, said on Wednesday the conflict would not be resolved peacefully as long as Assad's opponents were bent on his exit.
"Everything runs up against the opposition members' obsession with the idea of the overthrow of the Assad regime. As long as this irreconcilable position remains in force, nothing good will happen, armed action will continue, people will die," Foreign Minister Sergei Lavrov told a news conference.
Moscow has vetoed three U.N. Security Council resolutions aimed at pressuring Assad to step down or seek a negotiated end to the conflict, and divided world powers have been unable to halt the violence.
U.N. humanitarian chief Valerie Amos said their failure had led to a catastrophic humanitarian situation in Syria.
"What we are seeing now are the consequences of the failure of the international community to unite and to resolve the political crisis after nearly two years," she told reporters at the Davos World Economic Forum.
Sunni Muslim Gulf states have supported Assad's opponents and called for them to be armed, but the rebels complain that they have few weapons to challenge Assad's air power.
Saudi Arabia's former intelligence chief Prince Turki al-Faisal said Arab countries could not give game-changing weapons.
"Most weapons capable of dealing with the air force or long range artillery are manufactured by others and sold to Arab countries with strict restrictions on third party transfers," he told reporters at the World Economic Forum in Davos.
"Saudi Arabia can't give them because it has to get permission from the United States. I assume that other countries that have such weapons face similar restrictions."
President Vladimir Putin told Lebanon's visiting President Michel Suleiman on Wednesday that Moscow could offer financial and humanitarian aid to help Lebanon cope with 200,000 refugees who have crossed into his country from Syria. (Additional reporting by Timothy Heritage and Thomas Grove in Moscow, Jonathon Burch in Istanbul, Paul Taylor in Davos, Adrian Croft in Brussels and Oliver Holmes in Beirut; Writing by Alexander Dziadosz; Editing by Myra MacDonald)