Kerry flies to Geneva for delayed Syria talks with Russia

US Secretary of State John Kerry flew in to Geneva on Friday for a single day of talks with his Russian counterpart, seeking a deal with Moscow to restore a ceasefire in Syria.

Kerry had been scheduled to travel on Thursday, but delayed his departure over "technical" differences that would make it impossible to clinch a deal.

His Russian counterpart, Sergei Lavrov, travelled to Geneva as scheduled on Thursday, holding an hour of talks with US Syria envoy Staffan de Mistura.

Kerry and Lavrov headed into closed-door talks on Friday morning after a brief press conference in which they discussed North Korea's missile test overnight.

After an apparent change of mind over the worth of holding talks at all, the US Secretary of State had set off for Switzerland early on Friday.

Senior officials travelling with Kerry said on Friday that he would not have travelled to join Lavrov unless he thought there was a chance of making progress.

But they warned they could not guarantee a final agreement would be reached within the narrow window available before both men return home later in the day.

Washington wants Moscow to take concrete steps to force its Syrian ally Bashar al-Assad to lift a newly renewed siege on the city of Aleppo.

"We need to see a situation where it's clear within whatever is being agreed with the Russians that there won't be a siege of Aleppo," a senior US official told reporters

In exchange for reining in Assad, Russia wants closer military cooperation with the US to battle militant groups fighting in Syria.

Washington and Moscow are key backers of opposing sides in the Syrian conflict - but they are also joint leaders of the international effort to end the war, and declared a UN-backed ceasefire as far back as February.

But the truce collapsed and President Vladimir Putin's Russia has maintained strong support for Assad's forces, while Washington has encouraged the opposition rebels.

Kerry and Lavrov have continued to meet, most recently on Sunday and Monday on the sidelines of the G20 in China, where Putin also talked to US President Barack Obama.

But fighting has continued on the ground, with Assad's Russian-backed forces encircling and attempting to choke rebel-held areas of Syria's biggest city, Aleppo, and rebels launching a wide-scale offensive in the western province of Hama.