(Adds two Iranian sources on Geneva 1, Saudis, more background)
By Parisa Hafezi
ANKARA, Jan 20 (Reuters) - Iran said on Monday it had accepted "without preconditions" an invitation by U.N. Secretary-General Ban Ki-moon to attend talks due to start on Wednesday in Switzerland aimed at ending Syria's civil war, the student news agency ISNA reported.
But in comments that may complicate Iran's participation, two Iranian sources said Tehran's attendance at the talks, known as 'Geneva 2', did not mean it backed a plan for Syria's political transition agreed at a Geneva conference in June 2012.
Western and Gulf Arab nations say they have been reluctant to support the idea of Iran participating at all in the Geneva 2 talks this week in the city of Montreux because it is supporting Assad militarily and has never backed the 2012 transition plan.
The United States and its allies say this plan means Assad would have to step down.
"We have always rejected any precondition for attending the Geneva 2 meeting on Syria ... Based on the official invitation that we have received, Iran will attend the Geneva 2 without any preconditions," ISNA quoted Foreign Ministry spokeswoman Marzieh Afkham as saying.
Iranian lawmaker Abbasali Mansouri was more explicit, according to the semi-official Fars news agency.
"Iran will never accept the Geneva 1 as precondition for attending the talks in Switzerland," he was quoted as saying.
"The key to solving the Syrian crisis is in Iran's hands," Mansouri added.
Fars also quoted an unnamed source as saying Iran's presence at the Montreux talks did not imply its acceptance of the Geneva 1 agreement.
FRENCH, SAUDI SCEPTICISM
France said on Monday that Iran should not be allowed to attend the Syria peace talks if it did not accept the creation of a transitional government with full executive powers.
Saudi Arabia, which has strongly backed groups fighting Assad's forces, also believes Iran should not attend because of its stance on Geneva 1 and its military support for Assad, the Saudi Press Agency quoted an "official source" as saying.
U.N. Secretary-General Ban said on Sunday he had spoken at length with Iranian Foreign Minister Mohammad Javad Zarif in recent days and that he believed Tehran did support the Geneva 2012 plan for the Syria talks.
Ban said Zarif had assured him Iran would play a "positive and constructive role in Montreux".
Some 130,000 people have been killed and a quarter of all Syrians driven from their homes in the civil war, which began with peaceful protests against 40 years of Assad family rule and has descended into a sectarian conflict, with the opposing sides armed and funded by Sunni Arab states and Shi'ite Iran. (Writing by Parisa Hafezi; Editing by Gareth Jones)