The United States accused Russia of ignoring the facts surrounding a poison gas attack in Syria, highlighting tensions between the West and Moscow over how to eliminate the country's chemical weapons.
Despite a weekend agreement between the Cold War rivals aimed at dismantling Syria's chemical arsenal by mid-2014, the two sides remain poles apart in their assessment of the August 21 gas attack which left hundreds dead.
Russia insists the attack on the Damascus suburb of Ghouta was a "provocation" by opponents fighting Syria President Bashar al-Assad's regime designed to trigger military strikes by the United States.
The United States and France maintain the attack was carried out by Syrian government forces, and believe an assessment by UN experts released on Monday backed their view.
On Tuesday, after meeting French counterpart Laurent Fabius in Moscow, Russian Foreign Minister Sergei Lavrov repeated Moscow's allegation that the August 21 attack was carried out by Syrian rebels.
Lavrov said the UN report "proves that chemical weapons were used" but not that the Assad regime was behind it.
Russia still has "most serious basis to believe that this was a provocation," Lavrov said of the attack.
He called on world powers not to "play up emotions" when making decisions, but rather "rely on professionals."
The United States dismissed Lavrov's comments emphatically, however, exposing the entrenched differences between the West and Moscow.
"When you look at the details of the evidence they present -- it is inconceivable that anybody other than the regime used" the chemical weapons, US President Barack Obama said Tuesday of the UN report.
The report helped "change the international dynamic" on the issue, he claimed in the interview on the Spanish language Telemundo network.
Earlier, Fabius said a "difference in approach" existed between France and Russia on the methods required to reach peace but the two sides were "perfectly agreed" on the need for a political solution.
The Moscow talks came a day after France, the United States and Britain said they will push for a strong resolution at the UN.
Diplomats said France and Britain are preparing a draft that will demand a threat of sanctions if Assad does not comply with the chemical disarmament plan.
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However, Lavrov stressed that the agreement he reached with American counterpart John Kerry Saturday meant that the resolution will not be under the chapter of the UN charter that allows the use of force.
"The resolution... will not invoke Chapter VII," he said, in comments that were echoed later Tuesday by Russia's deputy foreign minister after a meeting with Syria's foreign minister in Damascus, according to the official SANA news agency.
Yet, this position is a direct a reversal of Lavrov's remarks Sunday, in which he specifically suggested any breach of chemical weapons agreements by Syria could prompt "measures according to Chapter VII of the United Nations charter."
Chapter VII can also impose mandatory economic sanctions against a target government.
Washington insisted Tuesday a Chapter VII resolution remained an option under the terms of the weekend agreement.
UN chief Ban Ki-moon is to meet with the foreign ministers of the five key nations in New York on the sidelines of the UN General Assembly, and three days later, with the top diplomats of the US and Russia, to help resolve the Syria crisis, he said Tuesday.
Ban said the attacks with banned chemical weapons were only the "tip of the iceberg," and urged the major powers to take a "broader" look to tackle the fighting as well as the humanitarian strife.
The United Nations permanent Security Council members held new negotiations on Tuesday on the wording of a resolution to back the Russia-US accord.
Diplomats said ambassadors discussed a French text which included a demand for action under Chapter VII if Assad does not stick to the plan.
France also wants chemical weapons attacks in Syria referred to the International Criminal Court. The meeting broke up however with no agreement.
The United States had moved to the brink of a military strike on Syria after blaming Assad's regime for the attack which it said left 1,400 people dead.
The strike however was put on hold last week as Syria agreed to a fast-track accession to the international convention banning chemical weapons, formally agreed by the US and Russia in Geneva.
The 30-month long conflict in Syria has killed more than 110,000 people, according to rights groups, and refugees have flooded countries in the region and beyond, with Bulgaria on Tuesday appealing for EU help in accommodating the influx.
Seven million people are in urgent need of humanitarian aide, and $4.4 billion are needed to help those displaced by the violence, the UN Emergency Relief coordinator Valerie Amos said Tuesday.