Syrian rebels have called a truce brokered by the US and Russia a practical failure as the ceasefire expired and reinvigorated fighting restarted across the country.

Rebel leaders have said one of the principal aims of the ceasefire – the delivery of aid to besieged civilians in eastern Aleppo – was not achieved.

"I believe that practically it has failed and has ended," Zakaria Malahifji, head of the political office of the Aleppo-based group Fastaqim, told Reuters news agency.

"There is no hope," he said regarding the possible arrival of aid. "It has been a number of days of procrastination. Every day there is a pretext. There is no hope of aid being delivered currently."

One UN 20-truck aid convoy meant to go to Aleppo never made it across the Turkish border. The convoy, which had enough supplies to feed tens of thousands of people, was persistently blocked by the Syrian government in Damascus and not give the proper permissions and guarantees to travel, according to the UN.

"I am pained and disappointed that a United Nations convoy has yet to cross into Syria from Turkey, and safely reach eastern Aleppo," the UN under secretary general for humanitarian affairs Stephen O'Brien said in a statement.

Up to 275,000 people remain trapped in the eastern part of the city without food, water, proper shelter or medical care, he added.

The 20-truck convoy would have been the first of two that would have carried flour and other food supplies, enough to feed some 185,000 people for one month, he said.

Rebel sources reported as the ceasefire ended on its sixth day that they were preparing to restart their offensives. According to the Syrian Observatory for Human Rights, fighting had begun in many of Syria's main urban centres including Aleppo, Rif Dimashq, Idlib, Homs, Hama, Latakia, Damascus and Al-Raqqah.

Video shared on social media by the UK-based group showed shows destruction caused by regime forces' shelling on areas of the al-Sa'en al-Aswad village in the northern countryside of Homs with reports of eight killed in subsequent clashes. Four barrel bombs dropped by helicopters killed 10 in the Dael in Daraa province, the observatory added.