The United Nations on Wednesday, 21 September, said it is set to resume humanitarian aid convoys after a strike on aid trucks killed at least 20 people and prompted the UN to suspend deliveries on Tuesday.

The UN special envoy to Syria, Staffan di Mistura said aid trucks would start rolling out to some areas but "carefully and cautiously."

The UN Office for the Coordination of Humanitarian Affairs (OCHA) added in a statement: "The preparation for these convoys has now resumed and we are ready to deliver aid to besieged and hard-to-reach areas as soon as possible. The United Nations continues to call for safe, unconditional, unimpeded and sustained access to all Syrians in need, wherever they are."

A spokesperson for the OCHA, Jens Laerke, said numerous convoys were expected as early as Thursday, 22 September, but did not specify the areas the convoys would reach.

US Secretary of State John Kerry urged that all planes be grounded in the key areas of Syria to save a nationwide ceasefire that had been called for, while addressing the UN Security Council on Wednesday. He added that the attack on the convoy "raised profound doubts" on whether Russia and Syria would be committed to the ceasefire obligations.

"How can people go sit at a table with a regime that bombs hospitals, drops chlorine gas again and again and again and again, and acts with impunity? What kind of credibility do you have? Supposedly we all want the same goal ... a secular united Syria ... but we are all proving to be woefully inadequate to come to the table and have that discussion."

He added, "You're supposed to sit there and have happy talk in Geneva while the regime drops bombs?"

The UK-based Syrian Observatory for Human Rights said the attack was an air strike and if it was proved to be true, it could incriminate Russia or Syria, because neither the opposition nor the Islamist groups have air power.

The announcement to resume aid convoys comes amid accusations by the US that Russia was responsible for launching the air strike on the convoy. Moscow denied the accusation, while Russian Foreign Minister Sergei Lavrov said a "very thorough and impartial investigation" needs to be conducted to determine what had happened.

Lavrov told the Security Council, "Many have said it could have been a rocket or an artillery shelling. I think we need to refrain from emotional reactions and instead investigate and be very professional."

Syria aid convoy bombed
Damaged aid trucks are pictured after an air strike on the rebel-held town of Urm al-KubraAmmar Abdullah/Reuters