European splits emerge over Saudi attack as UN diplomacy begins

* France leads European push to defuse Iran-US tensions

* UK breaks ranks with Europeans by directly blaming Iran

* France careful not to point finger straight at Tehran

* British-French divergence may complicate diplomacy

By John Irish and Kylie MacLellan

UNITED NATIONS, Sept 23 (Reuters) - France and Britain were at odds on Monday over who to blame for an attack on Saudi Arabia's oil facilities, potentially complicating efforts to defuse tensions between the United States and Iran on the sidelines of the U.N. General Assembly.

France has led a European push to try to defuse tensions between Washington and Tehran and sees the annual gathering of global leaders that begins on Monday as an opportunity to revive diplomacy.

But those efforts have stalled, with Iran reducing its commitments to a 2015 nuclear deal with world powers, from which Washington withdrew last year, and the United States refusing to ease sanctions that have strangled its oil exports, a mainstay of the Iranian economy.

An attack on Saudi oil facilities, which the United States has blamed on Iran, has also complicated matters. Hopes at the end of August that Trump and Rouhani could meet at the United Nations now seem slim.

Speaking on his way to New York, British Prime Minister Boris Johnson appeared to break ranks with his European counterparts on Monday, apportioning blame directly on Iran for the attacks.

"The UK is attributing responsibility with a very high degree of probability to Iran for the Aramco attacks. We think it very likely indeed that Iran was indeed responsible," Johnson told reporters on the plane to the United Nations General Assembly in New York.

"We will be working with our American friends and our European friends to construct a response that tries to deescalate tensions in the Gulf region," he said.

Those words were in stark contrast to French officials, who have been extremely cautious not to point the finger directly at Tehran, fearing that it could escalate tensions.

"One must be very careful in attributing responsibility," French President Emmanuel Macron told Le Monde newspaper en route for New York, adding that he didn't want to be drawn into something that could escalate tensions.

The United States and Saudi Arabia have already blamed Iran for the Sept. 14 strikes that initially halved Saudi oil output. Yemen's Iran-aligned Houthi movement has claimed responsibility.

Macron's foreign minister said on Sunday that while the Houthi claims lacked credibility, there had to be a detailed a documented and investigation before formulating a response.

SHUFFLE DIPLOMACY

European powers party to the deal - France, Britain and Germany, known as the E3 - have remained united despite pressure from Washington, focusing their approach on seeking to bring Iran back into full compliance with the nuclear deal in return for economic relief and new negotiations.

Macron, Johnson and Angela Merkel hold a trilateral meeting later on Monday to coordinate their Iran strategy ahead of likely meetings with Trump and Rouhani.

Macron had pinned his efforts on offering Iran a $15 billion credit line that would enable it to eventually sell its oil, in return for which Iran would return to the deal and open a broader negotiation on its future nuclear activities, its ballistic missile program and regional influence.

That plan depended on the United States easing some sanctions, which it hasn't, and the attacks on Saudi Arabia have prompted Washington to impose more curbs, making Macron's diplomatic efforts even more complicated.

"The chances of a meeting have certainly not increased," Macron told Le Monde. "The Iranians are flexible on the terms but inflexible on the timing which, in their eyes, should come only at the end of the process, while the U.S. objective is to have this meeting in the near-term." (Reporting by John Irish, Editing by William Maclean)