* Official says harder to wring concessions from government
* Kerry: events on ground irrelevant to planned peace talks
* Assad says considering running in 2014 election
By Arshad Mohammed
PARIS, Oct 21 (Reuters) - The rise of Islamist groups fighting Syria's Western-backed rebels has emboldened the Syrian government and will make it harder to extract concessions from Damascus at any peace talks, a U.S. official said on Monday.
The United States hopes to bring moderate elements of the Syrian opposition together with the government at a peace conference tentatively expected next month in Geneva to try to end a two-and-a-half year civil war in which more than 100,000 people have died.
The talks face great obstacles, including divisions within the opposition, fighting between rival rebel groups and President Bashar al-Assad's reluctance to give up power.
Speaking ahead of a gathering of ministers from some of the so-called Friends of Syria group seeking to bolster the moderate opposition, a senior U.S. State Department official said that recent gains by Islamist groups would make the task harder.
Islamist groups such as Jabhat al-Nusra and the Islamic State of Iraq and the Levant (ISIL) have taken territory in parts of the north near the border with Turkey in recent weeks, forcing the Free Syrian Army (FSA) opposition force that is backed by some Western and Arab states to fight on two fronts.
"To me, the biggest single problem is that the regime probably feels more confident now because of the Islamic State of Iraq in Levant's actions on the ground," said the U.S. official, who spoke to reporters on condition of anonymity.
He said this had forced the FSA to sent fighters north to confront these groups, weakening it against the government.
"That has to give the regime comfort and confidence, and it will make the task of extracting concessions from the regime at the negotiating table more difficult," the official said.
KERRY: 'SITUATION ON GROUND IRRELEVANT'
U.S. Secretary of State John Kerry told reporters that events may have moved in Assad's direction since he and Russian Foreign Minister Sergei Lavrov announced plans for the peace conference in May, but he sought to play this down.
"The situation on the ground is irrelevant to the question of the implementation of Geneva 1," Kerry said, referring to a 2012 U.N.-backed document that sought to end the war by getting the two sides to choose a transitional government.
"It doesn't matter whether you are up or whether you are down on the battlefield, the objective of Geneva 2 remains the same ... a transition government arrived at by mutual consent of the parties," he added.
"I don't know anybody who believes that the opposition will ever consent to Bashar al-Assad being part of that government," he said. "If he thinks he is going to solve problems by running for re-election, I can say to him ... this war will not end."
In a confident and animated performance on a Syrian television interview, Assad indicated he had no intention of quitting, saying he might run for re-election in 2014.
"Personally, I don't see any obstacles to being nominated to run in the next presidential elections," Assad told Syria's Al Mayadeen TV when asked if he thought it was suitable to hold the election, as scheduled, next year.
A number of officials, including Arab League chief Nabil Elaraby, have said they expect the "Geneva 2" conference to be held on Nov. 23, though the United States, Russia and the United Nations have all said no date has been officially set.
Kerry will travel to London on Tuesday for a meeting of the so-called "London 11" nations seeking to bolster the Syrian opposition - to try to lay the groundwork for Geneva 2.
Britain, Egypt, France, Germany, Italy, Jordan, Qatar, Saudi Arabia, Turkey, the United Arab Emirates and the United States will discuss the agenda for the meeting and how to help the opposition prepare for it, the U.S. official said.
While Washington has said it is open to the possibility of Iran, which has supported Assad, coming to a Geneva conference, Kerry said it was hard to see Tehran playing a constructive role without its backing the idea of a transitional government.