By Louis Charbonneau
LAUSANNE, Switzerland, April 1 (Reuters) - It is one of those concepts that is particularly odious to Russia -- an automatic trigger mechanism under which the U.N. Security Council would be forced to do something.
Now a dispute over that issue threatens to wreck marathon negotiations on a preliminary political framework for a future comprehensive deal that would end the 12-year standoff over Iran's nuclear ambitions. The other major sticking point is Tehran's demands to continue pursuing nuclear centrifuge research and development
The dispute is this. Negotiators from six world powers - the United States, Britain, France, Germany, Russia and China - and Iran are struggling to come up with plan under which Iran would curb its most sensitive nuclear activities for at least 10 years in exchange for a gradual end to United Nations, U.S. and European Union sanctions.
Suspending U.S. and EU financial and energy sanctions measures will be relatively easy, analysts and diplomats say. And such measures can be quickly reimposed in the event of non-compliance by Iran, Western officials close to the talks say.
It is a different matter with U.N. Security Council sanctions, a myriad of measures detailed in four legally binding resolutions from between 2006 and 2010: a travel ban and asset freeze blacklist for individuals and entities, bans on trade in nuclear and missile technology, an arms embargo and other steps.
U.S. and European negotiators are willing to start suspending some U.N. sanctions if a deal is reached, possibly by initially removing some names from the U.N. blacklist. But they want any easing of U.N. sanctions to be automatically reversible -- negotiators call this a "snapback" -- if Tehran fails to comply with the terms of an agreement. And they will keep "proliferation-relevant" measures in place.
The problem is the snapback. It's the old battle of the "automatic trigger" mechanism for U.N. action that Russia has always opposed, because it would undermine its veto. Russia has never made any secret of its position on the issue.
Russia, which along with China, Britain, France and the United States is a veto-wielding permanent member of the 15-nation Security Council. Traditionally Moscow guards its veto rights jealously, as do the other four. It is one of the main sources of Russia's leverage as a major global diplomatic power.
"Russia has never been ready to give up its veto power and the status that gives it," said Mark Fitzpatrick, of the International Institute for Strategic Studies in London.
"It doesn't want to forgo any future decision to play a role in either impeding American diplomacy or possibly playing a card positively in the future," he added. "They don't want to give up leverage now that could be useful in the future."
It is a central issue in the case of Iran. If Tehran fails to comply with a nuclear agreement and Western powers decide that U.N. sanctions should be reimposed, if there is no trigger, a new Security Council resolution would be required. And sanctions resolutions can be a tough sell for Russia and China.
In such a case, Western diplomats say, Russia could, and most likely would, veto any attempt to restore U.N. sanctions on Iran. As a result, any so-called temporary relief involving U.N. nuclear sanctions or other U.N. measures would be permanent.
De facto permanence of U.N. sanctions relief would be a major problem for Republican-controlled Congress, who believe President Barack Obama's administration is going too far in offering possible sanctions relief to Tehran.
"Russia is now under U.S. and EU sanctions over its mischief in Ukraine and I can't see them being very helpful in the future on Iran if it breaks its obligations, something Iran has been known to do in the past," a Western official told Reuters.
U.S., British, French and German officials are pushing hard on the snapback issue. But Russia and Iran, backed by China, oppose automaticity. Western officials said they hoped for a compromise but offered no details on what a compromise formula could look like.
"U.N. lawyers have a lot of imagination and creativity," said one senior Western diplomat. "We have one solution in mind, but need to be sure the Russians are ok with it."
Past attempts by Western powers to insert automatic trigger clauses in resolutions on Iraq, Kosovo or Iran have failed in the face of Russian resistance.
The veto is vital for Moscow. After the dissolution of the Soviet Union in 1991, the Russian Federation was eager to take over the permanent Soviet seat in the U.N. Security Council. Along with the status, Moscow inherited the considerable Soviet foreign debt, which proved to be a major burden in the late 1990s when the Russian financial crisis erupted.
Over the years, Moscow has repeatedly used its veto power to protect allies, most recently in the case of Syrian President Bashar al-Assad. Russia, with China's support, has struck down three resolutions threatening Assad's government with sanctions and one calling for an International Criminal Court referral.
As Russia was moving to annex Ukraine's Black Sea territory of Crimea last year, Moscow vetoed a Security Council resolution that would have declared illegal an impending Crimean referendum on joining Russia. The result was that Crimea chose annexation, though Western powers condemned the vote. (Additional reporting by John Irish; Editing by Giles Elgood)