Istanbul, Turkey ? Kofi Annan is tinkering with a radical idea for reviving his moribund peace plan for Syria — a road map for political transition there that would be negotiated through a “contact group” that could include, among other nations, Russia and Iran.

The former secretary-general’s new plan was outlined Tuesday by a diplomat who is familiar with the U.N. mission. The proposal, which is expected to be presented to the Security Council later this week, comes as Annan’s peace mediation with President Bashar al-Assad appears to have hit a dead end in Damascus, leading to growing concerns that the Syria crisis will spiral into all-out civil war.

What’s intriguing about Annan’s new approach is that it could give Russia and Iran, the two key supporters of Assad’s survival, some motivation to remove him from power, and also some leverage to protect their interests in a post-Assad Syria. This would also make the plan controversial, with Israel and Saudi Arabia asking why the U.N. would give the mullahs in Tehran a share of the diplomatic action.

The reason Annan is said to be considering this unconventional approach is that nothing else has worked. The United States and its key Western allies don’t want to intervene militarily, fearing that this could produce a highly unpredictable and unstable outcome. The West wants Russia to broker a deal but so far President Vladimir Putin hasn’t seen enough pragmatic benefit to embrace this course.

To break the deadlock, Annan would create his contact group, composed of the permanent members of the Security Council (Britain, China, France, Russia and the United States), plus Saudi Arabia and perhaps Qatar to represent the Arab League, plus Turkey and Iran. The idea is to bring together the countries with most influence on the situation.

This unwieldy group would then draft the transition plan and take it to Assad and the Syrian opposition. This road map would call for a presidential election to choose Assad’s successor, plus a parliamentary ballot and a new constitution — with a timeline for achieving these milestones.

Assad would presumably depart for Russia, which is said to have offered him exile; the Syrian dictator is rumored to have transferred $6 billion in Syrian reserves to Moscow already. Under this scenario, Assad presumably could avoid international prosecution for war crimes. Iran is also said to have offered exile to Assad and his family.

To contain the bloodletting that would follow Assad’s ouster, Annan is said to favor a detailed plan for reforming the security forces, similar to reforms in Eastern Europe after the fall of communism.

The Russians’ participation could help stabilize Syria during the transition, because they might get buy-in from the Syrian military, many of whose senior officers are Russia-trained.

Would Russia or Iran support this unconventional proposal? It’s impossible to know. In recent days, the U.S. is said to have held exploratory talks with Russian officials who apparently have indicated some interest. Russia’s foreign minister, Sergei Lavrov, said a week ago that Moscow wasn’t wedded to Assad’s remaining in power, but the Russians have done nothing to move the Syrian dictator toward the exit.

As for Tehran, the Iranians have been signaling recently through various channels that, as part of any diplomatic settlement of the nuclear issue, they may want a parallel process to deal with regional issues. Annan’s contact group would address this Iranian desire.

If Annan’s idea for a contact group proves to be a non-starter, there aren’t any obvious alternatives, other than a deepening civil war. Assad last week resisted the former secretary-general’s de-escalation proposals, such as withdrawing Syrian troops from conflict zones and releasing political prisoners. And if progress isn’t made soon, Annan probably will have to abandon his peace effort — with all sides understanding this means a bloody war to the finish.

Who will bell the cat? That, in colloquial language, has been the puzzle for more than a year in the push to oust Assad. The Arab League wants a U.N. peacekeeping force, but it won’t happen. Saudi Arabia and Qatar have been arming the Sunni opposition and urging the U.S. to mount a major covert action. But that proposal scares the Obama administration and most of its Western allies. What does that leave for an option? Annan appears to have come up with a new idea.