The United Nations mediator in the Syrian conflict has called on the United States and Russia to try to salvage and renew a cessation of hostilities.

The call by Staffan de Mistura follows an intensification in fighting in many areas of the Middle Eastern nation.

Mr de Mistura issued a statement after meeting US Secretary of State John Kerry and Saudi Foreign Minister Adel al-Jubeir in Geneva.

The statement said "There can be no progress in the political process unless we urgently see tangible benefits on the ground for the Syrian people,"

He is also to meet with Russian Foreign Minister Sergei Lavrov in Moscow tomorrow.

Earlier, Mr Kerry said talks are closer to extending a Syrian truce to Aleppo, the divided northern city where sharp escalation of violence in recent weeks has torpedoed peace talks and left a ceasefire in tatters.

The first major ceasefire of the five-year Syrian war was put in place in February with US and Russian backing but has since all but collapsed.

Syria announced temporary local truces in other areas last week but has so far failed to extend it to Aleppo, where government air strikes and rebel shelling have killed hundreds of civilians in the past week, including more than 50 people in a hospital that rebels say was deliberately targeted.

The Aleppo fighting threatens to wreck the first peace talks involving the warring parties, which are due to resume at an unspecified date after breaking up in April when the opposition delegation walked out in anger.

"We're getting closer to a place of understanding, but we have some work to do, and that's why we're here," Mr Kerry said at the start of the meeting with Saudi Arabia's Foreign Minister Adel al-Jubeir.

The civil war in Syria has killed hundreds of thousands of people, driven millions from their homes, created the world's worst refugee crisis and provided a base for so called Islamic State militants who have launched attacks elsewhere.

The fighting has drawn in global powers and regional states, while all diplomatic efforts to resolve it have foundered over the fate of President Bashar al-Assad, who refuses to accept opposition demands that he leave power.

The US and Russia have taken the leading roles in the latest diplomatic initiative, which began after Moscow joined the war last year with an air campaign that tipped the balance of power in favour of Mr Assad, its ally.

So far, Syria has announced a "regime of calm" – a temporary local truce – in the Eastern Ghouta suburb of Damascus and the countryside of northern Latakia province, from Saturday morning.

The Latakia truce was for three days and the Ghouta truce, initially for 24 hours, was also extended by another 48.

Both are areas where there has been heavy fighting, but Aleppo remains the biggest prize for Mr Assad's forces, who are hoping to take full control of the city, Syria's largest before the war.

The nearby countryside includes the last strip of the Syria-Turkish border in the hands of Arab Sunni rebels.

A Russian military official, General Sergei Kuralenko, said talks were under way on extending the regime of calm to Aleppo.