FACTBOX: Options for tougher sanctions against Iran

(Reuters) - Western powers angered over Iran's belated disclosure of a second uranium enrichment plant will redouble efforts to slap harsher sanctions on Tehran if nuclear talks set for Thursday in Geneva prove fruitless.

But the six-power unity key to mustering truly tough U.N. Security Council sanctions envisaged by the United States, Britain, France and Germany remains elusive with Russia taking a wait-and-see stance and China again insisting on negotiations.

Following is a rundown of salient points.

SANCTIONS OPTIONS

* The United States, Britain and Germany suggest expanded sanctions should target Iran's paramount revenue earner, the oil and gas industry. Washington has looked at cutting off the 40 per percent of its gasoline stocks Iran must import due to a lack of domestic refining capacity.

But this proposal is unlikely to fly in Europe in the near future due to concerns it would harm not Iran's elite but ordinary Iranians and rally them anew behind a hardline Islamic leadership beset by unrest over alleged election fraud.

* More viable shorter-term options may be sanctions on foreign investment in Iran's oil and gas and import-export sectors, blacklisting more Iranian banks and firms run by the Revolutionary Guards, divesting from firms that trade with Iran, and banning export credits.

* Existing sanctions could be implemented more rigorously than the leaky regime now in place. These sanctions entail asset freezes and travel bans on Iranian firms and individuals and a ban on trade benefiting Iran's nuclear and missile programs.

INCREASED WESTERN RESOLVE

* Protracted high-level inertia about what to do with Iran, beyond threats of more sanctions that looked increasingly stale, yielded to a fresh sense of fresh urgency following last week's revelation of the second enrichment site.

* France said Iran was heading down a "dangerous" path and had until December to desist or get hit with wider sanctions.

* Britain blasted Iran's "serial deception" on key issues.

* U.S. President Barack Obama said Iran was "breaking rules that all nations must follow" and if the talks did not work, the powers would be "in a much stronger position to, for example, apply sanctions that bite."

RUSSIA REAPPLYING THE BRAKES

* Obama said last Wednesday he and Russian counterpart Dmitry Medvedev agreed further sanctions should be looked at if Iran proved obdurate in coming talks. "Sanctions are seldom productive but they are sometimes inevitable," said Medvedev.

Russia has since backpedaled from even cautious talk of sanctions. "I am convinced restraint is needed," said Foreign Minister Sergei Lavrov, without saying what he meant.

Lavrov reflects the views of Medvedev's predecessor, Vladimir Putin, now prime minister but still Russia's paramount leader and a hard-liner wedded to Russian geo-political interests which include significant sales of military hardware to Iran.

CHINA THE TOUGHEST HOLDOUT

China has said the disclosure of Iran's second enrichment site is worrying but urged partners to focus on negotiations as the only way to a comprehensive lasting settlement with Iran.

"We believe that all sides should take more steps to ease tensions and resolve problems, and not the opposite," Foreign Ministry spokesman Jiang Yu said on Monday, obliquely rebuking Western pressure for more sanctions.

China's position is a creature of its thirst for Iranian oil. China is on the hook to Iran for 12 percent of its crude oil imports. State-run Chinese firms also export gasoline to Iran, filling a void left by Western exporters who backed out under political pressure from their capitals.

WHAT'S NEXT FOR SANCTIONS?

No decision is in the pipeline before the end of the year. The next batch of sanctions will be watered down by Russia and China as previous rounds were, barring undeniable proof emerging of Iranian nuclear weapons activity. The extent of new sanctions will be influenced by the assessment of U.N. anti-proliferation inspectors, who have yet to visit the new enrichment site.

(Editing by Samia Nakhoul)