The United Nations Security Council was set for a showdown over Syria on Wednesday after Britain sought authorisation for Western military action that Russia called premature.
UN chemical weapons experts investigating an apparent gas attack that killed hundreds of civilians in rebel-held suburbs of Damascus made a second trip across the front line to take samples. Secretary-General Ban Ki-moon pleaded for them to be given the time they need to complete their mission.
But the US and European and West Asian allies have already pinned the blame on President Bashar al-Assad's forces. Even if Russia blacks UN approval, US-led air or missile strikes on Syria look all but certain, though the timing is far from clear.
That has set Western leaders on a collision course with Moscow, Assad's main arms supplier, as well as with China, which also has a veto in the Security Council and disapproves of what it sees as a push for Iraq-style "regime change" - despite US denials that President Barack Obama aims to overthrow Assad.
Uncertainty over how the escalation of the conflict at the heart of the oil-exporting West Asia will affect trade and the world economy sent oil prices to their highest levels in six months, while stocks fell. Fears over the economy of Syria's hostile neighbour Turkey pushed its lira to a record low.
Prime Minister David Cameron said Britain would propose a resolution on Wednesday at the Security Council in New York, seeking authority to take "necessary measures" to protect Syrian civilians. Sure of a veto, it seemed part of diplomatic strategy to isolate Moscow and rally a broad coalition behind Washington.
"We've always said we want the UN Security Council to live up to its responsibilities on Syria. Today they have an opportunity to do that," Cameron said in a statement.
Foreign Minister Sergei Lavrov said earlier in the day that any attack would be folly. One of his deputies responded to Cameron by saying the Council should wait for the UN inspectors' report.
"It would be premature, at the least, to discuss any Security Council reaction until the UN inspectors working in Syria present their report," Vladimir Titov said.
Ban pleaded for unity in the Security Council after more than two years of paralysis during which Syria's civil war has split West Asia on sectarian lines and fuelled rival camps in the world body along divisions that echo the Cold War.
"Syria is the biggest challenge of war and peace in the world today," Ban said in a speech at The Hague.
