US Secretary of State Hillary Clinton on Thursday condemned the latest onslaught of violence sponsored by the regime in Syria and said President Bashar al-Assad had to go.
"The regime-sponsored violence that we witnessed in Hama yesterday (Wednesday) is simply unconscionable," she told reporters.
A solution to the Syria crisis required a ceasefire, a transfer of power and the formation of a representative interim government, she added.
"Assad must transfer power and depart Syria," she said after a late night strategy session with Arab and Western powers on how to increase the pressure on the Damascus regime and bring about political change.
Clinton acknowledged that the United States had not yet been successful in bringing about international action that would have an impact on Assad.
"We have to reiterate our unity, we have to send a clear message to other nations that are not yet working with us, or even actively supporting the Assad regime, that there is no future in that," she said.
"And indeed planning for an orderly transition will be an important step."
The intensifying diplomacy comes against the backdrop of fresh reports of massacres in Syria and growing fears in the region of a descent into a destabilizing civil war.
The views aired in Istanbul were expected to be taken up again Thursday at the United Nations when the Security Council meets to hear special envoy Kofi Annan's report on his battered peace plan.
And Clinton is sending her special representative on Syria, Fred Hoff, to Moscow on Thursday to sound out the Russians, the official said.
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"She made clear that we want to work with Russia, but that we've got to have a common vision," a senior State Department official said after the gathering with Arab and Western power.
On Wednesday, Russia and China rejected any moves to remove Assad from power in a joint statement after two days of meetings between Russian President Vladimir Putin and Chinese leaders.
"Russia and China are decisively against attempts to regulate the Syrian crisis with outside military intervention, as well as imposing ... a policy of regime change," Russia and China said in a joint statement issued Wednesday.
Hosted by Turkish Foreign Minister Ahmet Davutoglu, the late night meeting included top officials from the EU, the United States, Britain, France, Germany, Spain, Italy, Jordan, Egypt, Saudi Arabia, Kuwait, UAE, Qatar, Tunisia, Morocco and Turkey.
They discussed calls made by some countries for invoking Chapter VII of the UN charter, which authorizes member states to take "all necessary measures" to carry out specific UN Security Council decisions. It can be used in some cases to authorize military action.
"The secretary made clear Chapter VII remains on the table at the appropriate time," the official said, briefing reporters on condition of anonymity.
France and Britain have already rejected as a non-starter a Russian proposal for an international conference that would include Syrian ally Iran.
Clinton told reporters Wednesday she would reserve judgment, but added, referring to Iran: "It's a little hard to imagine inviting a country that is stage managing the Assad regime's assault on its people."
The Syrian opposition reported that as many as 100 people, including women and children, were massacred Wednesday in a village in central Syria.
The Syrian Observatory for Human Rights tentatively put the number of dead at 87. The Syrian government has denied any involvement.