Russian and US efforts to resuscitate a Syrian ceasefire that collapsed after seven days remain stalled.
US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov met on the sidelines of the UN General Assembly a day after both took part in an acrimonious session of the International Syria Support Group.
"We exchanged some ideas and we had a little bit of progress. We're evaluating some mutual ideas in a constructive way," Kerry said of his talks on Friday with Russia's top diplomat.
Both the US and Russia say the ceasefire accord Kerry and Lavrov announced two weeks ago in Geneva offers the only realistic chance for progress toward ending a conflict that has claimed more than 400,000 lives since the spring of 2011.
But the atmosphere between the two great powers has grown frosty following a US airstrike last weekend that killed scores of Syrian government troops - attributed by the US to a mistake - and Monday's attack on a Syrian Red Crescent aid convoy, which left at least 20 dead.
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The US accuses Russia of bombing the convoy. The Russians deny any involvement and demand a "thorough and impartial" investigation.
Kerry said this week that restoring the shattered truce will require a major gesture on the part of the Syrian government and its allies, demanding the establishment of a no-fly zone over areas controlled by the opposition.
In an address on Friday to the General Assembly, Lavrov made it clear that Russia will not accede to Kerry's demand, insisting instead on the responsibility of the US and it allies to separate "so-called moderate opposition from terrorists".
Under the plan adopted in Geneva, the cease-fire was supposed to lead to co-operation between the US and Russia in mounting co-ordinated airstrikes against groups such as Islamic State and al-Nusra Front.
