By Samia Nakhoul and Khaled Yacoub Oweis
GENEVA (Reuters) - Syria peace talks were in disarray on Tuesday before they began, buffeted by a botched U.N. invitation to Iran, an explosion in Beirut and new evidence that appears to show Bashar al-Assad's government has tortured and killed thousands.
U.N. Secretary-General Ban Ki-moon's unexpected, last-minute decision on Sunday to invite President Assad's main foreign backer Iran - only to withdraw the invitation a day later - proved a diplomatic fiasco, undermining talks that are already given little chance of success.
War crimes lawyers said photographs apparently smuggled out of Syria by a military police photographer were clear evidence Assad's government has systematically tortured and killed some 11,000 detainees. One of three former international war crimes prosecutors who signed the report compared the images from Syria to the "industrial-scale killing" of Nazi death camps.
A suicide bomber killed four people in Beirut, capital of Lebanon, showing the urgent danger of sectarian violence spilling to Syria's neighbors, three years into a civil war that has already killed at least 130,000 people inside Syria.
The peace conference set to begin on Wednesday will include the first talks between Assad and his opponents. But hopes of a breakthrough are negligible at a time when fighting has escalated and neither side shows any sign of retreating from its demands or being able to end the war with a victory.
Around a third of Syria's 22 million people have been driven from their homes, many to refugee camps abroad; half are in desperate need of international aid. The country at the heart of the Middle East has been carved up on ethnic and sectarian lines, with neighbors and distant powers lining up to arm and fund rival factions.
It has been 18 months since a previous international peace conference in Geneva ended in failure, and all other diplomatic initiatives have also proven fruitless.
"At best, Geneva 2 will reconfirm agreements made during the first Geneva conference, call for ceasefires, maybe prisoners swap and so on," said one Western diplomat.
"At the same time, those taking part in the talks are de facto giving legitimization to Damascus. They are talking to Assad's government on the other side of the table.
"And so the show would go on while Assad stays in power."
The opposition says the talks, actually taking place in Montreux on Wednesday, must seek Assad's removal from power; he says the only subject to discuss should be fighting terrorists, the label he uses for all his armed opponents.
The opposition team due to arrive in Switzerland on Tuesday is headed by Ahmed Jarba, leader of the opposition National Coalition, which only agreed to attend at the last minute and nearly pulled out on Monday over Ban's invitation to Iran.
On the rebel side, the talks could increase the already ferocious internal strife among rival factions. The conference is being boycotted by the powerful Sunni Islamist factions that control territory inside Syria. They have denounced the exiled political opposition as traitors for attending.
The main ethnic Kurdish faction, which controls a large swathe of the northwest, has not been invited.
BAN'S GAFFE
The U.N. secretary-general arrived in Geneva on Tuesday ahead of the talks, having nearly torpedoed them with his botched invitation to Iran.
His aides shielded him from journalists' questions about the affair, which ended with a dispute over whether Iran had agreed to pre-conditions to attend.
Western countries have long insisted Tehran sign up to the final statement from the previous Geneva conference in 2012 before it could attend other talks.
Ban said Iran's foreign minister had told him Tehran accepted the 2012 statement, which includes a requirement that Syria set up a transitional government. But Tehran said it had agreed to no such thing. The Syrian opposition threatened to pull out of the conference and Western countries demanded Ban withdraw the invitation.
A Western diplomat described the day as "a real mess" and said Ban had made a gaffe that had almost led to the entire conference being cancelled and replaced with a bilateral meeting between Russia and the United States.
Iranian Deputy Foreign Minister Abbas Araqchi blamed Washington for the confusion. "We had repeatedly said that Iran would not accept any precondition," he told state television.
"We were willing to participate at the Geneva 2 conference, but because of America's illogical persistence on imposing preconditions on Iran, we will not take part."
PHOTOGRAPHS
The bleak humanitarian consequences of the war were illustrated starkly in photographs of the emaciated and abused bodies of detainees, released in a report by London law firm Carter Ruck, hired by Qatar, a supporter of Assad's foes.
The report, by three senior lawyers who have worked for international war crimes tribunals and three forensic experts, said they believed the pictures and the photographer's account were credible evidence Assad's government had systematically tortured and killed as many as 11,000 detainees.
They said they had been shown a cache of 55,000 images, most of which were provided by a source who identified himself as a Syrian police photographer whose job included documenting deaths in Assad's jails on behalf of the authorities.
The man, who sometimes had to photograph 50 bodies a day, had defected with digital copies of the images, and the lawyers believed he was a credible source.
"The bodies he photographed since the civil war began showed signs of starvation, brutal beatings, strangulation and other forms of torture and killing," the lawyers wrote. "In some cases the bodies had no eyes."
One of the authors, Desmond de Silva, former chief prosecutor of a war crimes tribunal for Sierra Leone and one of Britain's top lawyers, said the evidence documented "industrial-scale killing" reminiscent of Nazi death camps.
"Some of the images we saw were absolutely reminiscent of pictures of people who came out of Belsen and Auschwitz," de Silva said. "It is the tip of the iceberg because this is 11,000 in just one area."
"This is not to say that the people on the other side have been free of serious crime. I think there is evidence that has led very responsible people to say there have been crimes committed on both sides," he said.
"But this industrial killing of people in detention in our view is clearly that of the government."
Syria's war has worsened sectarian conflict across the Middle East, threatening to surge beyond its borders to its neighbors. Assad, a member of the Alawite offshoot of Shi'ite Islam, is backed by Shi'ite Iran and Lebanon's Hezbollah Shi'ite militia. His foes, mainly Sunni Muslims, are backed by Sunni powers Saudi Arabia and Qatar.
The conflict has heightened friction between the West and Russia and threatens to reignite civil wars in neighboring Iraq - where al Qaeda-linked Sunni militants allied to those in Syria have seized cities in recent weeks - and Lebanon, which has seen a surge of bombings and assassinations.
Tuesday's suicide bombing killed four people in Haret Harek, a residential neighborhood of Beirut known as a Hezbollah stronghold. The district was also the target of car bomb earlier this month that killed five people.
(Additional reporting by Stephanie Nebehay in Geneva, Garbiella Baczynska in Moscow, John Irish in Paris, Guy Faulconbridge in London, Laila Bassam, Alexander Dziadosz and Stephen Kalin in Beirut, and Isabel Coles in Erbil; Writing by Peter Graff; Editing by Alastair Macdonald)