Syria crisis

Jets pounded rebel positions in the city on Wednesday night as a week-old truce collapsed, reportedly killing at least 13 people.

It is unclear whether the new offensive will involve ground troops.

Talks between the US and Russia on reviving the collapsed ceasefire have broken up without progress in New York.

Russia and the US support Syria's government and opposition respectively.

"All the evidence we have points to that conclusion," one of the officials said.

The White House position is that Russia is responsible, whether it was Russian planes -- or the Syrian regime's -- that carried out Monday night's attack.

The aid convoy was hit in the area of Urum al-Kubra, west of Aleppo, prompting the United Nations to halt its aid operations in Syria.

Several people were injured, the UK-based Syrian Observatory for Human Rights said, but it did not say who carried out the strikes.

Russia has said the future of the truce is in doubt after the US-led coalition struck the Syrian army in Deir al-Zour.

A Syrian political adviser told the BBC the US strike could not be a mistake.

The cessation of hostilities brokered jointly by the US and Russia does not exclude attacks on IS or other jihadist groups.