* U.S., Turkey discussed measures to aid rebels at weekend
* Ambassador says legal, practical obstacles to buffer zone
ISTANBUL, Aug 15 (Reuters) - There are serious legal and practical obstacles to setting up a buffer zone or a no-fly zone in Syria, Turkish newspapers on Wednesday quoted the U.S. ambassador to Ankara as saying, after the two countries discussed the issue at the weekend.
Secretary of State Hillary Clinton said on Saturday the United States and Turkey were looking at all measures to help Syrian rebel forces fighting to overthrow President Bashar al-Assad, including a no-fly zone.
A NATO-led no-fly zone and bombing campaign helped Libyan rebels overthrow Muammar Gaddafi last year. But the United States and its European allies have been reluctant to take an overt military role in Syria's 17-month-old conflict.
U.S. Ambassador Francis Ricciardone said in a briefing with Turkish newspapers that issues such as setting up a no-fly zone or a buffer zone in Syria were easy to discuss but hard to realise.
"Of course we should evaluate these issues. However, our discussions of these issues with Turkey should not suggest we are making commitments to set up these zones," Ricciardone was reported as saying by the daily Taraf.
"There are serious legal and practical obstacles on this issue," he was quoted as saying. An official transcript of his comments, which were published by several papers in Turkish, was not immediately available.
"We will work on the subjects of a transition phase and buffer zone within the U.N. Security Council in line with international law," he was reported as saying.
Clinton had told reporters after talks with Turkish Foreign Minister Ahmet Davutoglu on Saturday that their countries needed to get into detailed operational planning on how to assist the rebels and bring a halt to the violence.
Asked if discussions included options such as imposing a no-fly zone over territory that Syrian rebels claim to control, Clinton indicated that was a possible option.
The rebels are believed to be getting weapons from Saudi Arabia and Qatar, but only non-lethal assistance from the United States.
Washington sees Turkey, one of Assad's harshest critics, as the key player both in supporting Syria's opposition and in planning for what U.S. officials say is the inevitable collapse of the Syrian leader's rule.
Meanwhile, Turkish television CNN Turk also quoted the U.S. ambassador as saying that Iran, a close ally of Syria, was providing weapons for Assad's forces, but the Iranian embassy in Ankara issued a statement denying it.
"The Embassy of the Islamic Republic of Iran in Ankara denies the U.S. ambassador to Ankara's statements targeting Iran and all kinds of claims about Iran providing weapons to terror organisations," it said.