A convoy of Red Crescent aid trucks has been hit in an airstrike near Aleppo, as a week-long ceasefire in Syria was declared over by the country's military.
The Red Crescent said the convoy had been making a delivery from Aleppo to rural rebel-held areas with unconfirmed reports from opposition activists the Local Co-Ordination Committees of Syria that 32 people had been killed and wounded in the attack near the town of Urm al-Kubra.
A UN spokesman said at least 18 of 31 trucks had been hit with UN Special Envoy for Syria, Staffan de Mistura, saying it was an "outrage".
"The convoy was the outcome of a long process of permission and preparations to assist isolated civilians," he said in a statement emailed to Reuters.
The British-based Syrian Observatory for Human Rights (SOHR) said it was not clear if the jets were Syrian or Russian.
A statement posted on the Facebook page of the Local Co-Ordination Committees of Syria said: "Martyrs and wounded among civilians were reported, some of them are still stuck under the rubble, in Aleppo city and its suburbs, due to bombardment and artillery shelling, just after Assad's regime had declared the ceasefire expired."
The fragile truce collapsed after accusations of breaches on both sides. Four US-led airstrikes mistakenly killed around 60 Syrian soldiers although the US say they believed were Islamic State (Isis) jihadists.
Earlier, the Ministry of Defence has said that a British drone was involved in an airstrike that killed dozens of Syrian troops.
The RAF Reaper aircraft was operating with aircraft from the US, Australia and Denmark near the eastern city of Deir ez-Zour on Saturday (17 September).
An MOD spokesman said: "We can confirm that the UK participated in the recent coalition air strike in Syria, south of [Deir ez-Zour] on Saturday, and we are fully co-operating with the coalition investigation," an MoD spokesman said, adding: "The UK would not intentionally target Syrian military units."
Russia has been backing Bashar-al-Assad's Syrian Army in their war against rebels in Aleppo – where 275,000 people remain trapped in the eastern part of the city without food, water, proper shelter or medical care, according to estimates.
During the truce up to 40 trucks filled with aid remained at the Turkish border waiting to be taken to the embattled city.