UNITED NATIONS (AP) — Against the backdrop of a new massacre in Syria, international envoy Kofi Annan on Thursday will propose tasking a group of world powers and key regional players including Iran to come up with a strategy to end the 15-month conflict, U.N. diplomats said.

Annan will present the United Nations with a plan for creating a “contact group” whose final proposal must be acceptable to Syria’s allies Russia and China, which have blocked all U.N. action, as well as the U.S. and its European allies, who insist that President Bashar Assad must go, they said.

There has also been talk about a meeting of key world leaders on the sidelines of the G20 summit in Mexico later this month to discuss the growing crisis in Syria and possible next steps, the diplomats said, speaking on condition of anonymity because consultations have been private.

“It’s time for all of us to turn our attention to an orderly transition of power in Syria that would pave the way for democratic, tolerant, pluralistic future,” U.S. Secretary of State Hillary Clinton told reporters Wednesday before leaving Azerbaijan for Turkey.

The violence in Syria has grown increasingly chaotic in recent months, and it is difficult to assign blame for much of the bloodshed. The government restricts journalists from moving freely, making it nearly impossible to independently verify accounts from either side. The opposition blames government forces and militias that support them known as shabihas while the government blames rebels and “armed terrorist groups.”

At the U.N., diplomats are increasingly concerned that the country is spiraling toward civil war.

Annan, the joint U.N.-Arab League envoy, will give his latest assessment of the Syrian conflict at an open meeting of the U.N. General Assembly on Thursday morning along with U.N. Secretary-General Ban Ki-moon, Arab League chief Nabil Elaraby, and a representative of U.N. human rights chief Navi Pillay. Annan will then brief the U.N. Security Council behind closed doors Thursday afternoon and have dinner with ambassadors from the council’s five permanent nations — the U.S., Russia, China, Britain and France, a council diplomat said.

Reports by Syrian activists of a surge of bloodshed in the central Hama province late Wednesday, with at least 23 people killed — and possibly many more — are bound to reinforce the growing belief that Annan’s six-point peace plan is unraveling.

The violence comes on the heels of a horrific massacre on May 25 and 26 in Houla, a cluster of villages in the central Homs province, which left over 100 dead including many women and children gunned down in their homes. U.N. investigators blamed pro-government gunmen for at least some of the killings but the Syrian regime denied responsibility and blamed rebels for the attacks.

U.S. Ambassador Susan Rice warned last week that the worst but most probable scenario in Syria is a failure of Annan’s peace plan and a spreading conflict that creates “a major crisis” not only in Syria but also region-wide. To avoid this, Rice urged Syria to implement the plan and if it doesn’t she said the Security Council should set aside its differences and increase the pressure on Syria with sanctions.

U.S. Treasury Secretary Timothy Geithner followed up Wednesday, warning Syria that U.N. sanctions may be near and calling for the world to exert “maximum financial pressure” on Assad’s government.

Russia and China, however, who have vetoed two resolutions threatening possible sanctions, issued a joint statement after a summit in Beijing reiterating their opposition to any outside military interference or forceful imposition of “regime change” in Syria. The statement also indicated opposition to U.N. sanctions.

Russia’s Foreign Minister Sergey Lavrov told reporters in Beijing on Wednesday that Moscow is proposing an international conference on Syria to try to persuade all Syrian opposition groups to respect Annan’s plan, end all violence and sit down for talks.

“Russia considers it essential to fulfill Kofi Annan’s peace plan along with the U.N. Security Council resolution that approved this plan,” Lavrov said in remarks posted on the Russian Foreign Ministry’s website.

“We believe that it’s necessary to convene a meeting of the countries which have a real influence with various opposition groups” including the permanent members of the U.N. Security Council, Turkey, Iran, the Arab League, the Organization of Islamic Cooperation and the European Union, he said.

While Lavrov focused on getting the divided opposition to implement the Annan plan, Clinton in recent days has been trying to open the door to a compromise with Russia, calling Assad’s ouster a necessary outcome of any political transition but not necessarily a “precondition.” The nuance suggests the U.S. is willing to allow Assad to hang on in power for part of a structured regime change.

Key nations have also been working on trying “to bind Russia into some sort of transition strategy on Syria,” a U.N. diplomat said, pointing to Clinton’s contacts with Lavrov, British Foreign Secretary William Hague’s visit to Moscow and Russian President Vladimir Putin’s visits to Germany and France.

U.N. diplomats said the key to the success of any Annan initiative is whether it can get all parties behind a transition strategy, and that still remains a distant goal.

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Associated Press Writer Bradley Klapper contributed to this report from Azerbaijan

Copyright 2012 The Associated Press.