* Syrian opposition war crimes blamed on foreign fighters
* Free Syrian Army trying to instil human rights law
* Divide in opposition puts pressure on peace plan
* Foreign fighters may be target of "second war"
By Tom Miles
GENEVA, Sept 16 (Reuters) - War crimes blamed on the Syrian opposition are predominantly being carried out by foreign fighters, a U.N. human rights investigator said on Monday, highlighting a deepening rift in the opposition that has been an obstacle to peace talks.
"If you're going to look for the (opposition) groups that are committing the worst crimes, look particularly for the foreign fighters, where the foreign fighters are fighting," Karen Koning Abuzayd told reporters in Geneva.
By contrast, Salim Idris, head of the Western-backed Supreme Military Council that oversees a loose grouping of rebels known as the Free Syrian Army, was trying to "infuse human rights law" and train soldiers in the rules of war, she said.
Abuzayd is one of the four lead members of the U.N. Commission of Inquiry on Syria, a body set up by the U.N. Human Rights Council two years ago to investigate war crimes and crimes against humanity in the Syrian conflict.
Although most of the commission's evidence has implicated forces loyal to President Bashar al-Assad, its reports this year have directed increasing suspicion to opposition groups and are frequently cited by supporters of President Bashar al-Assad.
The commission's contrasting views of Syria's domestic opposition and the Jihadist foreign fighters may add to pressure on efforts to bring all parties to the conflict together for peace talks at a so-called "Geneva 2" conference.
Paulo Pinheiro, chairman of the U.N. Commission of Inquiry on Syria, said there were now foreign fighters from about 20 countries in Syria including some from Europe.
U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov hope to agree a date for the conference when they meet in New York at the end of September. International mediator Lakhdar Brahimi is currently seeking to convene all parties possibly around mid-October.
The conference guidelines set out by major powers in June 2012 require all parties to agree to a ceasefire but leave it to the Syrian people alone to determine their future through a transitional authority. That gives the foreign fighters a duty to lay down their arms but no say in the running of Syria once the conflict is over, making them a potential new enemy.
"The Syrian fighters, they say that only the first of the wars is fighting the government, and the second one is getting rid of these people. They don't want them," said Abuzayd.
Louay Meqdad, a spokesman for the Free Syrian Army, said the Supreme Military Council was very clear and would not condone any crime in Syria. He said the Free Syrian Army was short of resources while militants were getting stronger, taking control of oilfields and other valuable areas.
"We should face the problem and find the solution. They are fighting against us, against the Free Syrian Army. They killed some of our commanders," he told Reuters in Istanbul.
Diplomats say regional powers such as Saudi Arabia and Qatar that are funding the foreign fighters must agree to stop supporting them in order for a peace deal to be struck at Geneva. In return, Syria's allies Iran and Russia would have to stop supplying weapons to Assad's government.
However, there would be a risk that foreign fighters would remain in Syria and keep fighting.
"We need somehow somebody who has contacts with these foreign fighters who represent them in some way or another," said a U.N. official.
"Stopping the violence entails stopping these people," said a diplomat who expects to be involved in any Geneva 2 talks.