US Secretary of State John Kerry said on Monday talks were closer to extending a Syrian truce to Aleppo, the divided northern city where a sharp escalation of violence in recent weeks has torpedoed peace talks.

Kerry was in Geneva for talks with other dignitaries to try to revive the first major ceasefire of the five-year Syrian war, which 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 them 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," Kerry said at the start of a meeting with Saudi Arabia's Foreign Minister Adel al-Jubeir.

After meeting Jubeir and UN envoy Staffan de Mistura, Kerry said he hoped for more clarity in the next day or so on restoring the nationwide ceasefire. The United States and Russia had agreed to keep extra staff in Geneva to work on it.

"Both sides, the opposition and the regime, have contributed to this chaos, and we are working over the next hours intensely in order to try to restore the cessation of hostilities," Kerry said. De Mistura said he would travel to Moscow for talks.

The civil war in Syria has killed hundred of thousands of people, driven millions from their homes, created the world's worst refugee crisis and provided a base for 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 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 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.

CIVILIANS KILLED

The opposition accuses the government of deliberately targeting civilians in rebel held parts of Aleppo to drive them out, and says the world must do more to force Damascus to halt air strikes.

For its part, the government says rebels have been heavily shelling government-held areas, proving that they are receiving more sophisticated weaponry from their foreign supporters, which include Arab states and Turkey.

A British-based monitoring group, the Syrian Observatory for Human Rights, has reported scores of civilians killed on both sides, although more in rebel-held territory.

Syrian state television said on Monday that a missile had hit the surroundings of Aleppo University Medical Hospital, and several civilians were injured by rebel mortar attacks on the residential area of Jamiyat Hay al Zahra in western Aleppo.

The rebel-held local council of Aleppo city announced a state of emergency in areas it runs due to the intense bombardment. About 350,000-400,000 people are believed to remain in rebel-held parts of what was once a city of 2 million.

Mohammad Muaz Abu Saleh, a senior councillor in the rebel Aleppo governate council, said residents were not abandoning opposition-held areas, despite the intense bombardment.

"Those who wanted to leave Aleppo have fled," he said. Those who have stayed behind "have decided to stay under all circumstances of shelling and siege. Aleppo will remain populated with its people not leaving."

Amar Al-Absi, a resident of a rebel-held area, said: "There was heavy shelling throughout the night. In my neighbourhood, Salah al-Deen, a missile hit a building that was empty and it was levelled but there were no casualties."

In the countryside north of Aleppo, other rebel groups have been fighting against Islamic State fighters, who are not party to any ceasefire.

Amaq, a news agency affiliated to Islamic State, said the militants had gained control of the villages of Doudayan, Tel Shaer and Iykda from rival rebels in the northern Aleppo area near the border with Turkey.

They said they were able cut the supply routes of other rebels in the area, despite Turkish artillery shelling to aid the rebels against Islamic State.

The Observatory said the militants had staged a counterattack to regain ground lost from other rebels in to-and-fro fighting that has seen no major gains for any side.

Turkey said it had shelled Islamic State positions across the border and attacked them with drones on Sunday, killing 34 militants in retaliation for cross-border strikes. The death toll could not be confirmed.

Turkey, a Nato ally, is part of a US-led coalition launching air strikes against Islamic State, but is also strongly opposed to the main Kurdish militia in Syria, Washington's closest ally on the ground. It is one of the leading opponents of Assad and backers of rebels opposed to him.

Another major supporter of the rebels is Saudi Arabia, whose Foreign Minister Jubeir blamed the latest escalation on the government, condemned it as a "violation of all humanitarian laws" and called for Assad to step down.

"He can leave through a political process, which we hope he will do, or he will be removed by force," Jubeir said alongside Kerry.  - Reuters